Memory device including multiple select gates and different bias conditions

ABSTRACT

Some embodiments include apparatuses and methods using first and second select gates coupled in series between a conductive line and a first memory cell string of a memory device, and third and fourth select gates coupled in series between the conductive line and a second memory cell string of the memory device. The memory device can include first, second, third, and fourth select lines to provide first, second, third, and fourth voltages, respectively, to the first, second, third, and fourth select gates, respectively, during an operation of the memory device. The first and second voltages can have a same value. The third and fourth voltages can have different values.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No.16/518,687, filed Jul. 22, 2019, which is a continuation of U.S.application Ser. No. 16/036,549, filed Jul. 16, 2018, now issued as U.S.Pat. No. 10,360,979, which is a continuation of U.S. application Ser.No. 15/669,311, now issued as U.S. Pat. No. 10,026,480, which is acontinuation of U.S. application Ser. No. 15/205,574, filed Jul. 8,2016, now issued as U.S. Pat. No. 9,728,266, all of which areincorporated herein by reference in their entireties.

BACKGROUND

Memory devices are widely used in computers and many electronic items tostore information. A memory device usually has numerous memory cells.The memory device performs a write operation to store information in thememory cells, a read operation to read the stored information, and anerase operation to erase information (e.g., obsolete information) fromsome or all of the memory cells. During these operations, an event suchas a leakage of current near the memory cells may occur. Such an eventmay reduce the efficiency of some operations (e.g., read and writeoperations) of the memory device. However, for other operations (e.g.,erase operations) of the memory device, such an event may be useful.Thus, designing a memory device and operating it to balance the effectof an event such as leakage current may pose a challenge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an apparatus in the form of a memorydevice, according to some embodiments described herein.

FIG. 2A shows a block diagram of a portion of a memory device includinga memory array having memory cell strings, select circuits, and doubledrain select lines, according to some embodiments described herein.

FIG. 2B shows a schematic diagram of the memory device of FIG. 2Aincluding double drain select gates, according to some embodimentsdescribed herein.

FIG. 2C shows a schematic diagram of a portion of the memory device ofFIG. 2B, according to some embodiments described herein.

FIG. 2D is a chart showing example values of voltages provided tosignals of the memory device of FIG. 2A through FIG. 2C during read,write, and erase operations of the memory device, according to someembodiments described herein.

FIG. 2E is a chart showing example values of voltages provided tosignals of a variation of the memory device of FIG. 2A through FIG. 2C,according to some embodiments described herein.

FIG. 2F shows a side view of a structure of a portion of the memorydevice of FIG. 2A through FIG. 2C, according to some embodimentsdescribed herein.

FIG. 2G shows a top view of the structure of the portion of the memorydevice of FIG. 2F, according to some embodiments described herein.

FIG. 2H shows details of a portion of the structure of the memory deviceof FIG. 2F including sidewalls of some of parts of the memory device,according to some embodiments described herein.

FIG. 2I through FIG. 2M show variations in distances between differentsidewalls of some parts of the memory device of FIG. 2H and variationsin thicknesses of select gates of the portion of memory device 200 ofFIG. 2H, according to some embodiments described herein.

FIG. 3A shows a block diagram of a portion of another memory deviceincluding double drain select lines and double source select lines,which can be a variation of the memory device of FIG. 2A, according tosome embodiments described herein.

FIG. 3B shows a schematic diagram of the memory device of FIG. 3Aincluding double drain select gates and double source select gates,according to some embodiments described herein.

FIG. 3C shows a schematic diagram of a portion of the memory device ofFIG. 3B, according to some embodiments described herein.

FIG. 3D is a chart showing example values of voltages provided tosignals of the memory device of FIG. 3A through FIG. 3C during read,write, and erase operations of the memory device, according to someembodiments described herein.

FIG. 3E is a chart showing example values of voltages provided tosignals of a variation of the memory device of FIG. 3A through FIG. 3C,according to some embodiments described herein.

FIG. 3F shows a side view of a structure of a portion of the memorydevice of FIG. 3A through FIG. 3C, according to some embodimentsdescribed herein.

FIG. 3G shows a top view of the structure of the portion of the memorydevice of FIG. 3F, according to some embodiments described herein.

FIG. 4A and FIG. 4B show a schematic diagram and a structure,respectively, of a portion of a memory device including triple drainselect gates and triple source select gates, according to someembodiments described herein.

FIG. 5A through FIG. 16 show processes of forming memory deviceincluding multiple select gates, according to some embodiments describedherein.

FIG. 17 through FIG. 21 show processes of forming memory deviceincluding drain select gates, each having portions of differentresistances (e.g., a polycrystalline portion and a metal portion),according to some embodiments described herein.

FIG. 22 and FIG. 23 show processes of forming memory device includingdrain select gates, each having portions of different resistances (e.g.,a polycrystalline portion and a silicide portion), according to someembodiments described herein.

FIG. 24 show a memory device including drain select gates and sourceselect gates, each having portions of different resistances, accordingto some embodiments described herein.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of an apparatus in the form of a memorydevice 100, according to some embodiments described herein. Memorydevice 100 can include a memory array 102 having memory cells 103 thatcan be arranged in rows and columns along with lines (e.g., accesslines) 104 and lines (e.g., data lines) 105. Memory device 100 can uselines 104 to access memory cells 103 and lines 105 to exchangeinformation with memory cells 103.

Row access 108 and column access 109 circuitry can respond to an addressregister 112 to access memory cells 103 based on row address and columnaddress signals on lines 110, 111, or both. A data input/output circuit114 can be configured to exchange information between memory cells 103and lines 110. Lines 110 and 111 can include nodes within memory device100 or pins (or solder balls) on a package where memory device 100 canreside.

A control circuit 116 can control operations of memory device 100 basedon signals present on lines 110 and 111. A device (e.g., a processor ora memory controller) external to memory device 100 can send differentcommands (e.g., read, write, and erase commands) to memory device 100using different combinations of signals on lines 110, 111, or both.

Memory device 100 can respond to commands to perform memory operationson memory cells 103, such as performing a read operation to readinformation from memory cells 103 or performing a write (e.g.,programming) operation to store (e.g., program) information into memorycells 103. Memory device 100 can also perform an erase operation toerase information from some or all of memory cells 103.

Memory device 100 can receive a supply voltage, including supplyvoltages Vcc and Vss. Supply voltage Vss can operate at a groundpotential (e.g., having a value of approximately zero volts). Supplyvoltage Vcc can include an external voltage supplied to memory device100 from an external power source such as a battery or an alternatingcurrent to direct current (AC-DC) converter circuitry. Memory device 100can include a voltage generator 107 to generate different voltages foruse in operations of memory device 100, such as read, write, and eraseoperations.

Each of memory cells 103 can be programmed to store informationrepresenting a value of a fraction of a bit, a value of a single bit, ora value of multiple bits such as two, three, four, or another number ofbits. For example, each of memory cells 103 can be programmed to storeinformation representing a binary value “0” or “1” of a single bit. Thesingle bit per cell is sometimes called a single level cell. In anotherexample, each of memory cells 103 can be programmed to store informationrepresenting a value for multiple bits, such as one of four possiblevalues “00”, “01”, “10”, and “11” of two bits, one of eight possiblevalues “000”, “001”, “010”, “011”, “100”, “101”, “110”, and “111” ofthree bits, or one of other values of another number of multiple bits. Acell that has the ability to store multiple bits is sometimes called amulti-level cell (or multi-state cell).

Memory device 100 can include a non-volatile memory device, and memorycells 103 can include non-volatile memory cells, such that memory cells103 can retain information stored thereon when power (e.g., Vcc, Vss, orboth) is disconnected from memory device 100. For example, memory device100 can be a flash memory device, such as a NAND flash or a NOR flashmemory device, or another kind of memory device, such as a variableresistance memory device (e.g., a phase change or resistive RAM device).

Memory device 100 can include a memory device where memory cells 103 canbe physically located in multiple levels on the same device, such thatsome of memory cells 103 can be stacked over some other memory cells 103in multiple levels over a substrate (e.g., a semiconductor substrate) ofmemory device 100. One of ordinary skill in the art may recognize thatmemory device 100 may include other elements, several of which are notshown in FIG. 1, so as not to obscure the example embodiments describedherein.

At least a portion of memory device 100 can include structures similarto or identical to the memory devices described below with reference toFIG. 2A through FIG. 24.

FIG. 2A shows a block diagram of a portion of a memory device 200including a memory array 202 having memory cell strings 231 through 240,291, and 292, select circuits 241 through 252 and 241′ through 252′, anddouble drain select lines, according to some embodiments describedherein. Memory device 200 can correspond to memory device 100 of FIG. 1.For example, memory array 202 can form part of memory array 102 of FIG.1.

As shown in FIG. 2A, memory device 200 can include blocks (blocks ofmemory cells) blocks 203 ₀ and 203 ₁. Two blocks are shown as anexample. Memory device 200 can include many blocks (e.g., up tothousands or more blocks). Each of blocks 203 ₀ and 203 ₁ has its ownmemory cell strings and associated select circuits. For example, block203 ₀ has memory cell strings 231 through 236, and select circuits 241through 246 and 241′ through 246′. Block 203 ₁ has memory cell strings237 through 240, 291, and 292, and select circuits 247 through 252 and247′ through 252′.

Each of the memory cell strings 231 through 240, 291, and 292, can beassociated with (e.g., coupled to) two select circuits. For example,memory cell string 231 is associated with select circuit (e.g., topselect circuit) 241 and select circuit (e.g., bottom select circuit)241′. FIG. 2A shows an example of six memory cell strings and theirassociated circuits (e.g., top and bottom select circuits) in each ofblocks 203 ₀ and 203 ₁. The number of memory cell strings and theirassociated select circuits in each of blocks 203 ₀ and 203 ₁ can vary.

Memory device 200 can include lines 270, 271, and 272 that carry signalsBL0, BL1, and BL2, respectively. Each of lines 270, 271, and 272 can bestructured as a conductive line (which includes a conductive materialregion) and can form part of a respective data line (e.g., bit line) ofmemory device 200. The memory cell strings of blocks 203 ₀ and 202 ₁ canshare lines 270, 271, and 272. For example, memory cell strings 231,232, 237, and 238 can share line 270. Memory cell strings 233, 234, 239,and 240 can share line 271. Memory cell strings 235, 236, 291, and 292can share line 272. FIG. 2A shows three lines (e.g., data lines) 270,271, and 272 as an example. The number of data line can vary.

Memory device 200 can include a line 299 that can carry a signal SRC(e.g., source line signal). Line 299 can be structured as a conductiveline and can form part of a source (e.g., a source line) of memorydevice 200. Blocks 203 ₀ and 203 ₁ can share line 299.

Memory device 200 can include separate control lines in blocks 203 ₀ and203 ₁. As shown in FIG. 2A, memory device 200 can include control lines220 ₀, 221 ₀, 222 ₀, and 223 ₀ that can carry corresponding signals(e.g., word line signals) WL0 ₀, WL1 ₀, WL2 ₀, and WL3 ₀. Memory device200 can include control lines 220 ₁, 221 ₁, 222 ₁, and 223 ₁ that cancarry corresponding signals (e.g., word line signals) WL0 ₁, WL1 ₁, WL2₁, and WL3 ₁. Control lines 220 ₀ through 223 ₀ and 220 ₁ through 223 ₁can be structured as conductive control lines (which include conductivematerials) can form part of a respective access lines (e.g., word lines)of memory device 200 to access memory cells in a respective block. FIG.2A shows four control lines (220 ₀ through 223 ₀ or 220 ₁ through 223 ₁)in each of blocks 203 ₀ and 203 ₁ as an example. The number of controllines can vary.

As show in FIG. 2A, memory device 200 can include double (e.g., upperand lower) drain select lines, including select lines 281 _(A), 282_(A), 283 _(A), and 284 _(A) (e.g., upper drain select lines) and selectlines 281 _(B), 282 _(B), 283 _(B), and 284 _(B), (e.g., lower drainselect lines). Each of select lines 281 _(A), 282 _(A), 283 _(A), and284 _(A) can carry a separate (e.g., different) signal (e.g., an upperselect line signal) SGD_(A). Each of select lines 281 _(B), 282 _(B),283 _(B), and 284 _(B) can carry a separate signal (e.g., a lower selectline signal) SGD_(B). Memory device 200 can include select lines (e.g.,source select line) 281′, 282′, 283′, and 284′, and each can carry aseparate (e.g., different) signal SGS.

FIG. 2A shows select line 281 _(A) coupled to select lines 282 _(A)(through a connection 281″_(A)) and select line 283 _(A) coupled toselect lines 284 _(A) (through a connection 283″_(A)) to indicate anexample of memory device 200 where signal SGD_(A) associated with selectline 281 _(A) and signal SGD_(A) associated with select line 282 _(A)can be the same signal, and signal SGD_(A) associated with select line283 _(A) and signal SGD_(A) associated with select line 284 _(A) can bethe same signal. This means that signal SGD_(A) associated with selectline 281 _(A) and signal SGD_(A) associated with select line 282 _(A)can be provided (e.g., bias) with voltages having the same value; andsignal SGD_(A) associated with select line 283 _(A) and signal SGD_(A)associated with select line 284 _(A) can be provided (e.g., bias) withvoltages having the same value.

In a variation of memory device 200, signal SGD_(A) associated withselect line 281 _(A) and signal SGD_(A) associated with select line 282_(A) can be separate signals; and signal SGD_(A) associated with selectline 283 _(A) and signal SGD_(A) associated with select line 284 _(A)can be separate signals. Separate signals can be provided with voltageshaving different values at one point in time, but the separate signalscan also be provided with voltages having the same value at anothertime. In the variation of memory device 200, select lines 281 _(A) and282 _(A) can be uncoupled from each other; and select lines 283 _(A) and284 _(A) can be uncoupled from each other. Separate signals may allowmore precise bias conditions (e.g., precise voltage values) to beapplied (e.g., separately applied) to select lines 281 _(A), 282 _(A),283 _(A), and 284 _(A) during operations of memory device 200.

In the structure of memory device 200, connection 281″_(A) betweenselect lines 281 _(A) and 282 _(A) can be a direct connection (e.g.,physically connected to each other). As an example, in such a directconnection, select line 281 _(A) and 282 _(A) can be part of the samepiece of conductive material (e.g., a same layer of conductivematerial). Alternatively, connection 281″_(A) between select lines 281_(A) and 282 _(A) in FIG. 2A can be an indirect connection. For example,in the indirect connection, select lines 281 _(A) and 282 _(A) may notbe formed from the same piece (e.g., layer) of conductive material butthey can be connected (e.g., electrically connected) to each otherthrough a transistor (or through multiple transistors). Similarly, inthe structure of memory device 200, connection 283″_(A) between selectlines 283 _(A) and 284 _(A) can be a direct connection (e.g., formedfrom the same piece of conductive material) or an indirect connection(e.g., not formed from the same piece of conductive material). In someoperations (e.g., read and write operations) of memory device 200,providing the same signal (e.g., shared signal) to select lines 281 _(A)and 282 _(A) and providing the same signal (e.g., shared signal) toselect lines 283 _(A) and 284 _(A) may simplify operations of memorydevice 200.

As shown in FIG. 2A, select circuits 241, 243, and 245 can share selectline 281 _(A) and 281 _(B). Select circuits 242, 244, and 246 can shareselect line 282 _(A) and 282 _(B). Select circuits 247, 249, and 251 canshare select line 283 _(A) and 283 _(B). Select circuits 248, 250, and252 can share select line 284 _(A) and 284 _(B). Each of select circuits241 through 252 can include multiple select gates (e.g., multipletransistors, shown in FIG. 2B) that can be controlled (e.g., turned onor turned off) two respective select lines (e.g., 281 _(A) and 281 _(B),282 _(A) and 282 _(B), 283 _(A) and 283 _(B), or 284 _(A) and 284 _(B)).

Select circuits 241′. 243′, and 245′ can share select line 281′. Selectcircuits 242′, 244′, and 246′ can share select line 282′. Selectcircuits 247′, 249′, and 251′ can share select line 283′. Selectcircuits 248′, 250′, and 252′ can share select line 284′. Each of selectcircuits 241′ through 252′ can include a select gate (e.g., atransistor, shown in FIG. 2B) that can be controlled (e.g., turned on orturned off) by a respective select line among select lines 281′, 282′,283′, and 284′. In a variation of memory device 200 (e.g., shown in FIG.3B), each of select circuits 241′ through 252′ can include multipleselect gates (e.g., multiple transistors) that can be controlled bymultiple select lines (e.g., multiple source select lines).

In FIG. 2A, each of memory cell strings 231 through 240, 291, and 292has memory cells (shown in FIG. 2B) arranged in a string (e.g., coupledin series among each other) to store information. During an operation(e.g., read, write, or erase operation) of memory device 200, memorycell strings 231 through 240, 291, and 292 can be individually selectedto access the memory cells in the selected memory cell string in orderto store information in or read information from the selected memorycell string.

During an operation (e.g., read, write, or erase operation) of memorydevice 200, one or both select circuits associated with a selectedmemory cell string can be activated (e.g., by turning on the transistorsin the select circuits), depending on which operation memory device 200performs on the selected memory cell string. During an operation ofmemory device 200, memory device 200 can select a memory cell (amongmemory cells 210, 211, 212, and 213) of a particular memory cell stringas a selected memory cell in order to store information in (e.g., duringa write operation) or to read information from (e.g., during a readoperation) the selected memory cell. Thus, a selected memory cell stringis a memory cell string that has a selected memory cell. A deselected(unselected) memory cell string is a memory cell string that does nothave a selected memory cell. During a particular operation (e.g., reador write operation) of memory device 200, a selected block is a blockthat has a selected memory cell string; a deselected (unselected block)block is a block that does not have a selected memory cell string duringthat particular operation.

Activating a particular select circuit among select circuits 247 through252 during an operation of memory device 200 can include providing(e.g., applying) voltages having certain values to signals SGD_(A) andSGD_(B) associated with that particular select circuit. Activating aparticular select circuit among select circuits 247′ through 252′ caninclude providing (e.g., applying) voltages having certain values tosignal SGS associated with that particular select circuit. When aparticular select circuit among select circuits 241 through 252 isactivated, it can couple (e.g., form a current path from) a selectedmemory cell string associated with that particular select circuit to arespective data line (e.g., one of lines 270, 271, or 272). When aparticular select circuit among select circuits 241′ through 252′ isactivated, it can couple (e.g., form a current path from) a selectedmemory cell string associated with that particular select circuit to asource (e.g., line 299).

FIG. 2B shows a schematic diagram of memory device 200 of FIG. 2A,according to some embodiments described herein. For simplicity, onlyfour memory cell strings 231, 232, 237 and 238 and ten select circuits241, 242, 243, 245, 247, 248, 241′, 242′, 247′, and 248′ of FIG. 2A arelabeled in FIG. 2B. As shown in FIG. 2B, memory device 200 can includememory cells 210, 211, 212, and 213 and select gates (e.g., drain selecttransistors) 261 and 262 and select gates (e.g., source selecttransistors) 263 that can be physically arranged in three dimensions(3-D), such as x, y, and z dimensions, with respect to of the structure(shown in FIG. 2F and FIG. 2G) of memory device 200.

As shown in FIG. 2B, each of the memory cell strings (e.g., strings 231,232, 237 and 238) of memory device 200 can include one of memory cells210, one of memory cells 211, one of memory cells 212, and one of memorycells 213. FIG. 2B shows an example of four memory cells 210, 211, 212,and 213 in each memory cell string. The number of memory cells in eachmemory cell string can vary.

Each of select circuits 241, 242, 247, and 248 can include double selectgates (e.g., double drain select gates): one of select gates 261 and oneof select gates 262. Each of select circuits 241′, 242′, 247′, and 248′can include one of select gates 263. Each of select gates 261, 262, and263 can operated as a transistor, such as a field-effect transistor(FET). An example of an FET includes a metal-oxide semiconductor (MOS)transistor. A select line shared among particular select circuits can beshared by select gates of those particular select circuits. For example,select line 281 _(A) can be shared by select gates 261 of select circuit241 and select circuits 243, and 245. In another example, select line281 _(B) can be shared by select gates 262 of select circuit 241 andselect circuits 243, and 245. A select line (e.g., select line 281 _(A),282 _(A), 283 _(A), 284 _(A), 281 _(B), 282 _(B), 283 _(B), and 284_(B), 281′, 282′, 283′, and 284′) can carry a signal (e.g., signalSGD_(A), SGD_(B), or SGS) but it does not operate like a switch (e.g., atransistor). A select gate (e.g., select gate 262, 262, or 263) canreceive a signal from a respective select line and can operate like aswitch (e.g., a transistor).

In order to focus on the embodiments discussed herein, the descriptionbelow with reference to FIG. 2C through FIG. 2G focuses on four memorycell strings 231, 232, 237, and 238 select circuits 241, 242, 247, 248,241′. 242′, 247′, and 248′. Other memory cell strings and selectcircuits of memory device 200 have similar structures and connections.

FIG. 2C shows a schematic diagram of a portion of memory device 200 ofFIG. 2B including memory cell strings 231, 232, 237, and 238 and selectcircuits 241, 242, 247, 248, 241′, 242′, 247′, and 248′ and coupledbetween line 270 and line 299, according to some embodiments describedherein. As shown in FIG. 2C, select gates (e.g., double drain selectgates) 261 and 262 of each of select circuits 241, 242, 247, and 248 canbe coupled in series between line 270 and a respective memory cellstring among memory cell strings 231, 232, 237, and 238. Select gate 263of each of select circuits 241′, 242′, 247′, and 248′ can be coupledbetween line 299 and a respective memory cell string among memory cellstrings 231, 232, 237, and 238.

Select gate 261 of select circuit 241 has a terminal (e.g., a transistorgate) that can be part of (e.g., formed by a portion of) select line 281_(A). Select gate 262 of select circuit 241 has a terminal (e.g., atransistor gate) that can be part of (e.g., formed by a portion of)select line 281 _(B). Select gates 261 and 262 of select circuit 241 canbe controlled (e.g., turned on or turned off) by signals SGD_(A) andSGD_(B) provided to select lines 281 _(A) and 281 _(B), respectively.Select gate 263 of select circuit 241′ has a terminal (e.g., atransistor gate) that can be part of (e.g., formed by a portion of)select line 281′. Select gate 263 of select circuit 241′ can becontrolled (e.g., turned on or turned off) by signal SGS provided toselect lines 281′.

Similarly, as shown in FIG. 2C, select gates 261 and 262 of each ofselect circuits 242, 247, and 248 also have terminals (transistor gates)that can be parts of (e.g., formed by portions of) respective selectlines among select lines 282 _(A), 283 _(A), 284 _(A), 282 _(B), 283_(B), and 284 _(B). Select gate 263 of each select circuits 242′, 247′,and 248′ also has a terminal (transistor gate) that can be part of(e.g., formed by a portion of) a respective select line among selectline 282′, 283′, and 284′.

During an operation (e.g., a read or write operation) of memory device200, select gates 261, 262, and 263 of particular select circuitsassociated with a selected memory cell string can be activated (e.g.,turned on) to couple the selected memory cell string to a respectivedata line and the source. For example, in FIG. 2C, during a writeoperation of memory device 200, if memory cell string 231 is a selectedmemory cell string, then select gates 261 and 262 of select circuit 241can be activated to couple memory cell string 231 to line 270; selectgate 261 of select circuit 241′ may not be activated. In anotherexample, in FIG. 2C, during a read operation of memory device 200, ifmemory cell string 231 is a selected memory cell string, then selectgates 261 and 262 of select circuit 241 can be activated to couplememory cell string 231 to line 270; select gate 261 of select circuit241′ can also be activated to couple memory cell string 231 to line 270and line 299. In these two examples here, while memory cell string 231is selected, memory cell strings 232, 237, and 238 are deselected. Thus,select gates 261, 262, and 263 in select circuits 242, 247, 248, 242′,247′, and 248′ (associated with memory cell strings 232, 237, and 238)can be deactivated (e.g., turned off) to decouple memory cell strings232, 237, and 238 (deselected memory cell strings) from line 270 andline 299.

FIG. 2D is a chart 200D showing example values of voltages provided tosignals BL, SGD_(A), SGD_(B), WL selected, WL unselected, SGS, and SRCduring read, write, and erase operations of memory device 200, accordingto some embodiments described herein. As shown in FIG. 2D, in each ofthe read, write, and erase operations, the signals in chart 200D can beprovided with voltages having different values (in volt unit), dependingupon which block (selected or unselected block) and which memory cellstring (selected or unselected string) the signals are used.

In FIG. 2D, signal BL refers to the signal on a data line (e.g., one ofsignals BL0, BL1, and BL2 FIG. 2B) associated with a selected memorycell. Signal WL selected refers to the signal on a control line of aselected block that is associated with a selected memory cell. Signal WLdeselected refers to the signal on a control line of a selected blockthat is not associated with a selected memory cell. For example, ifblock 203 ₀ (FIG. 2C) is a selected block, and memory cell 212 of memorycell string 231 is a selected memory cell, then WL selected refers tosignal WL2 ₀ and WL deselected refers each of signals WL0 ₀, WL1 ₀, andWL3 ₀.

During a read or write operation, memory cell strings (e.g., strings231, 232, 237, and 238 in FIG. 2C) associated the same data line (e.g.,line 270) can be selected one at a time (e.g., sequentially selected).During an erase operation, memory cell strings in the entire selectedblock can be concurrently placed in the same bias condition (e.g.,biased using voltages of the same value) to erase information from thememory cell strings of the selected block.

In the example read, write, and erase operations of memory device 200(FIG. 2C) described below, the following assumptions are made. Block 203₀ is a selected block. Block 203 ₁ is a deselected block. Thus, allmemory cell strings of block 203 ₁ are deselected memory cell strings ofa deselected block. Memory cell string 231 of block 203 ₀ (selectedblock) is a selected memory cell string. Memory cell 212 of memory cellstring 231 (selected memory cell string) is a selected memory cell.Memory cell string 232 of block 203 ₀ (selected block) is a deselectedmemory cell string of a selected block. In this example, control line222 ₀ is a selected control line (associated with WL selected signal)because memory cell 212 of memory cell string 231 is a selected memorycell. Control lines 220 ₀, 221 ₀, and 223 ₀ are deselected control lines(associated with WL deselected signal) because memory cells 210, 211,and 213 of memory cell string 231 are not selected (deselected) memorycells. In this example, control lines 220 ₁, 221 ₁, 222 ₁, and 223 ₁ ofblock 203 ₁ (deselected block) can be provided with voltages having thesame values.

The following descriptions of example read, write, and erase operationsfocus on the values of voltages provided to signals SGD_(A) andSGD_(B)(FIG. 2C) of block 203 ₀ (selected block) and block 203 ₁(deselected block). Other signals of memory device 200 (e.g., BL, WLselected, WL deselected, SGS, and SRC) can be provided with voltageshaving example values shown in FIG. 2D, which are not described indetail in the following description to help focus on the descriptionherein.

During a read operation of memory device 200 (FIG. 2C) for a selectedblock (e.g., block 203 ₀), based on the above assumptions and as shownin chart 200D of FIG. 2D, signals SGD_(A) and SGD_(B) associated with aselected string of the selected block can be provided (e.g., bias) withvoltages having the same value, such as SGD_(A)=V1=5V and SGD_(B)=5V.Thus, in this example, select lines 281 _(A) and 281 _(B) (FIG. 2C)associated with memory cell string 231 (selected string) can be providedwith voltages having the same value of 5V. Hence, select gates 261 and262 of select circuit 241 can receive voltages having the same value of5V. In a read operation, signals SGD_(A) and SGD_(B) associated with adeselected string of the selected block can be provided with voltageshaving different values, such as SGD_(A)=V1=5V and SGD_(B)=V2=0V. Thus,in this example, select lines 282 _(A) and 282 _(B) associated withmemory cell string 232 (deselected string) can be provided with voltageshaving values of 5V and 0V, respectively. Hence, select gates 261 and262 of select circuit 242 can receive voltages having values of 5V and0V, respectively.

During a read operation of memory device 200 (FIG. 2C) for a deselectedblock (e.g., block 203 ₁), based on the above assumptions and as shownin chart 200D of FIG. 2D, signals SGD_(A) and SGD_(B) associated withall strings (e.g., string 237 and 238) of the deselected block can beprovided (e.g., bias) with voltages having different values, such asSGD_(A)=V3=0.5V and SGD_(B)=V4=0V. Thus, in this example, in block 203 ₁(deselected block), each of select lines 283 _(A) and 284 _(A) can beprovided with a voltage having a value of 0.5V; and each of select lines283 _(B) and 284 _(B) can be provided with a voltage having a value of0V. Hence, each of select gates 261 of select circuits 247 and 248 canreceive a voltage having a value of 0.5V; and each of select gates 262of select circuits 247 and 248 can receive a voltage having a value of0V.

During a write operation of memory device 200 (FIG. 2C) for a selectedblock (e.g., block 203 ₀), based on the above assumptions and as shownin chart 200D of FIG. 2D, signals SGD_(A) and SGD_(B) associated with aselected string can be provided (e.g., bias) with voltages having thesame value, such as SGD_(A)=V5=3V and SGD_(B)=3V. Thus, in this example,select lines 281 _(A) and 281 _(E) (FIG. 2C) associated with memory cellstring 231 (selected string) can be provided with voltages having thesame value of 3V. Hence, select gates 261 and 262 of select circuit 241can receive voltages having the same value of 3V. In a write operation,signals SGD_(A) and SGD_(B) associated with a deselected string can beprovided with voltages having different values, such as SGD_(A)=V5=3Vand SGD_(B)=V6=0V. Thus, in this example, select lines 282 _(A) and 282_(E) associated with memory cell string 232 (deselected string) can beprovided with voltages having values of 3V and 0V, respectively. Hence,select gates 261 and 262 of select circuit 242 can receive voltages of3V and 0V, respectively.

During a write operation of memory device 200 (FIG. 2C) for a deselectedblock (e.g., block 203 ₁), based on the above assumptions and as shownin chart 200D of FIG. 2D, signals SGD_(A) and SGD_(B) associated withall strings of block 203 ₁ can be provided (e.g., bias) with voltageshaving different values such as SGD_(A)=V7=2.3V and SGD_(B)=V8=0V. Thus,in this example, in block 203 ₁ (deselected block), each of select lines283 _(A) and 284 _(A) can be provided with a voltage having a value of2.3V; and each of select lines 283 _(B) and 284 _(B) can be providedwith a voltage having a value of 0V. Hence, each of select gates 261 ofselect circuits 247 and 248 can receive a voltage having a value of2.3V; and each of select gates 262 of select circuits 247 and 248 canreceive a voltage having a value of 0V.

During an erase operation of memory device 200 (FIG. 2C) for a selectedblock, based on the above assumptions and as shown in chart 200D of FIG.2D, signals SGD_(A) and SGD_(B) associated with a selected string and adeselected string can be provided with voltages having different values,such as SGD_(A)=V9=10V and SGD_(B)=V10=14V, or alternatively,SGD_(A)=V9=14V and SGD_(B)=V10=10V. Thus, in this example, in block 203₀, select lines 281 _(A) and 282 _(A) (FIG. 2C) can be provided withvoltages having values of 10V; and select lines 281 _(B) and 282 _(B)can be provided with voltages having values of 14V. Hence, select gates261 of select circuits 241 and 242 can receive voltages having values of10V; and select gates 262 of select circuits 241 and 242 can receivevoltages having values of 14V. Alternatively, in an erase operation,select lines 281 _(A) and 282 _(A) associated with memory cell string231 (selected string) and memory cell string 232 (deselected string) canbe provided with voltages having values of 14V; and select lines 281_(B) and 282 _(E) can be provided with voltages having values of 10V.Hence, select gates 261 of select circuits 241 and 242 can receivevoltages having values of 14V, and select gates 262 of select circuits241 and 242 can receive voltages having values of 10V. Memory device 200(FIG. 2A through FIG. 2C) may include dummy memory cells. In FIG. 2D, inerase operation portion. “5V-10V (DUMMY)” indicates a range of voltages(approximately 5V to 10V) that can be applied to the control lines(e.g., dummy word lines) of the dummy memory cells.

During an erase operation of memory device 200 (FIG. 2C) for adeselected block, based on the above assumptions and as shown in chart200D of FIG. 2D, select lines 283 _(A), 283 _(B), 284 _(A), and 284 _(B)(FIG. 2C) of block 203 ₁ (deselected block) may be placed in a “float”state (shown as “F” or “FLOAT” in FIG. 2D). In the float state, thevoltages on select lines 283 _(A), 283 _(B), 284 _(A), and 284 _(B) mayhave values proportional to the value of the voltage (e.g., a value ofapproximately 20V of an erase voltage (e.g., Verase)) provided to signalBL (e.g., signal BL0 in this example). Hence, select gates 261 of selectcircuits 247 and 248 of block 203 ₁ (deselected block) can be placed inthe float state in an erase operation.

The example read, write, and erase operation described above assumesthat block 203 ₀ is a selected block and block 203 ₁ is a deselectedblock. However, if block 203 ₀ is assumed to be a deselected block, thenselect lines 281 _(A) and 281 _(B) can be provided with voltages usedfor a deselected block described above. For example, if block 203 ₀ is adeselected block, based on chart 200D (FIG. 2D), select lines 281 _(A)and 281 _(B) can be provided with voltages having values of V3=0.5V andV4=0V respectively, during a read operation, or voltages having valuesof V7=2.3V and V8=0V, respectively, during a write operation, or beplaced in a float state with voltages having values of up to the valueof the voltage provide to signal BL (e.g., signal BL0).

FIG. 2E is a chart 200E showing example values of voltages provided tosignals BL, SGD_(A), SGD_(B), WL selected. WL unselected, SGS, and SRCof memory device 200 during read, write, and erase operations of memorydevice 200 when signal SGD_(A) associated with select line 281 _(A) andsignal SGD_(A) associated with select line 282 _(A) can be separatesignals (e.g., not shared) in a variation of memory device 200,according to some embodiments described herein. Chart 200E can be avariation of chart 200D of FIG. 2D. In chart 200D, signals SGD_(A)associated with select line 281 _(A) and signal SGD_(A) associated withselect line 282 _(A) can be a shared signal (e.g., the same signal). Inchart 200E, signals associated with select lines 281 _(A) and 282 _(A)are separate signals. Thus, in chart 200E, voltages of different valuescan be provide to signals SGD_(A) associated with select line 281 _(A)and signal SGD_(A) associated with select line 282 _(A) of a deselectedstring of a selected block.

For example, during a read operation of memory device 200 for a selectedblock (e.g., block 203 ₀), based on the above assumptions and as shownin chart 200E of FIG. 2E, signal SGD_(A) associated with select line 282_(A) of memory cell string 232 (deselected string) can be provided withvoltages having values of either V1=0V or V1=0.5V (instead of 5V as inchart 200D). This means that in a variation of memory device 200 whereselect line 281 _(A) is uncoupled to select line 282 _(A) during a readoperation, select gates 261 and 262 of select circuits 241 and 242 inFIG. 2B can receive voltages of different values of either 5V and 0V or5V and 0.5V, respectively.

During a write operation of memory device 200, signal SGD_(A) associatedwith select line 282 _(A) of memory cell string 232 (deselected string)can be provided with voltages having a value of either V5=0V or V5=2.3V(instead of 3V as in chart 200D). Hence, select gates 262 of selectcircuits 241 and 242 in FIG. 2B (when select line 281 _(A) is uncoupledto select line 282 _(A)) can receive voltages of different values ofeither 3V and 0V, respectively, or 3V and 2.3V, respectively. In anerase operation of memory device 200, the values of voltages provided tothe signals of memory device 200 based on charts 200E can be the same asthose based on chart 300E.

Using the biasing techniques based on chart 200D and chart 200E mayimprove operation of memory device 200 during read, write, and eraseoperations. Description of such improvements is described in below afterthe description of FIG. 2F through FIG. 2M.

FIG. 2F shows a side view of a structure of a portion of memory device200, according to some embodiments described herein. The structure ofmemory device 200 in FIG. 2E corresponds to the schematic diagram ofmemory device 200 shown in FIG. 2C. As shown in FIG. 2E, memory device200 can include a substrate 390 over which memory cells 210, 211, 212,and 214 of memory cell strings 231 and 232 (of block 203 ₀) and memorycell strings 231 and 232 (of block 203 ₁) can be formed (e.g., formedvertically with respect to substrate 390). Memory device 200 includesdifferent levels 309 through 315 (e.g., internal device levels betweensubstrate and line 270) with respect to a z-dimension. Memory cells 210,211, 212, and 213 can be located in levels 310, 311, 312, and 313,respectively (e.g., arranged vertically in the z-dimension with respectto substrate 390). Select gates 261, 262, and 263 of select circuits241, 241′, 242, and 242′ (of block 203 ₀) and select circuits 247, 247′,248, and 248′ (of block 203 ₁) can also be formed (e.g., formedvertically) over substrate 390.

Memory device 200 can include pillars 331, 332, 333, and 334 havinglengths extending outwardly (e.g., vertically) from substrate 390 in az-dimension of memory device 200. The select lines (e.g., upper andlower drain select lines and source select lines) associated with memorycell strings 231, 232, 237, and 238 can be located along a respectivepillar in the z-dimension as shown in FIG. 2E. For example, select lines281 _(A), 281 _(B), and 281′ associated with memory cell string 231 canbe located in along pillar 331 in a z-dimension.

FIG. 2G shows a top view of a structure of a portion of memory device200 of FIG. 2F, according to some embodiments described herein. As shownin FIG. 2G, lines 270, 271, and 272 (e.g., regions of conductivematerials of respective lines 270, 271, and 272) can have their lengthsextending in the x-dimension, which is perpendicular to the y-dimension.As shown in a cut-away view in FIG. 2G, select lines 281′, 282′, 283′,and 284′ have lengths extending in the y-dimension and are underneath(with respect to the z-dimension) select lines 281 _(B), 282 _(B), 283_(B), and 284 _(B), respectively. Select lines 281 _(B), 282 _(B), 283_(B), and 284 _(B) have lengths extending in the y-dimension and areunderneath select lines 281 _(A), 282 _(A), 283 _(A), and 284 _(A),respectively. Select lines 281 _(A), 282 _(A), 283 _(A), and 284 _(A)have lengths extending in the y-dimension and are underneath lines 270,271, and 272. FIG. 2G also show pillars 331, 332, 333, and 334 (whichcontacts the underside of line 270) and memory cell strings 231, 232,237, and 238 at locations relative to the locations of pillars 331,332.333, and 334. Other pillars (dashed circles) of memory device 200are not labeled. The side view (e.g., cross-sectional view) of memorydevice 200 in FIG. 2F is taken along section label 2F-2F of FIG. 2G.

Referring to FIG. 2F, substrate 390 of memory device 200 can includemonocrystalline (also referred to as single-crystal) semiconductormaterial. For example, substrate 390 can include monocrystalline silicon(also referred to as single-crystal silicon). The monocrystallinesemiconductor material of substrate 390 can include impurities, suchthat substrate 390 can have a specific conductivity type (e.g., n-typeor p-type). Although not shown in FIG. 2F, substrate 390 can includecircuitry that can be located directly under line 299 and pillars 331,332, 333, and 334. Such circuitry can include buffers (e.g., pagebuffers), decoders, and other circuit components of memory device 200.

As shown in FIG. 2F, line 270 (e.g., a data line that includes a regionof conductive material) can have a length extending in the x-dimension,which is perpendicular to a z-dimension. Line 299 can have a lengthextending in the x-dimension. FIG. 2F shows an example where line 299(e.g., source) can be formed over (e.g., by depositing a conductivematerial) a portion of substrate 390. Alternatively, line 299 can beformed in or formed on a portion of substrate 390 (e.g., by doping aportion of substrate 390).

Each of pillars 331, 332.333, and 334 can include a portion 343 coupledto line 270, a portion 346 coupled to line 299, a portion 344 betweenportions 343 and 346, and a portion 345 surrounded by portions 343, 344,and 346. Thus, each of pillars 331, 332, 333, and 334 is a pillar ofmaterials that includes materials of respective portions 343, 344, 345,and 346. Each of portions 343, 344, and 346 can include conductivematerial (e.g., doped polycrystalline silicon (doped polysilicon)).Portion 345 (e.g., a filler) can include dielectric material (e.g., anoxide of silicon, such as silicon dioxide). FIG. 2F shows an example ofwhere each of pillars 331, 332, 333, and 334 includes portion 345 (e.g.,dielectric material). Alternatively, portion 345 can be omitted, suchthat the material of portion 344 may also occupy the space occupied ofportion 345.

Portions 343 and 346 can include materials of the same conductivitytype. Portion 344 can include a material having a different conductivitytype from that of portions 343 and 346. For example, portions 343 and346 can include a semiconductor material of n-type (e.g., n-typepolycrystalline silicon), and portion 344 can include a semiconductormaterial of p-type (e.g., p-type polycrystalline silicon).Alternatively, portions 343, 344, and 346 can include materials of thesame conductivity type (e.g., n-type polycrystalline silicon).

Portion 344 and at least part of each of portions 343 and 346 can form aconductive channel in a respective pillar among pillars 331, 332, 333,and 334. The conductive channel can carry current (e.g., current betweenline 270 (e.g., data line) and line 299 (e.g., source) during anoperation (e.g., read, write, or erase) of memory device 200. FIG. 2Fshows an example where part of portion 343 can extend from line 270 to alocation in a respective pillar at approximately the level 315. However,part of portion 343 can extend from line 270 to any location in arespective pillar between level 313 and 315.

Memory cells 210, 211, 212, and 213 of memory cell string 231 can belocated along a segment of pillar 331 (e.g., the segment of pillar 331extending from level 310 to level 313). In a similar structure, memorycells 210, 211, 212, and 213 of memory cell strings 232, 237, and 238can be located along a of a respective pillar among pillars 332, 333,and 334, as shown in FIG. 2F.

Control lines 220 ₀, 221 ₀, 222 ₀, 223 ₀ (of block 203 ₀) and 220 ₁, 221₁, 222 ₁, and 223 ₁ (of block 203 ₁) associated with respective memorycells 210, 211, 212, and 213 can also be located in levels 310, 311,312, and 313, respectively, along a segment (e.g., the segment ofextending from level 310 to level 313) of a respective pillar amongpillars 332, 333, and 334, as shown in FIG. 2F. The materials of controllines 220 ₀, 221 ₀, 222 ₀, 223 ₀ (of block 203 ₀) and 220 ₁, 221 ₁, 222₁, and 223 ₁ (of clock 203 ₁) can include a conductive material (e.g.,conductively doped polycrystalline silicon of n-type, metals, or otherconductive materials). Thus, as shown in FIG. 2F, control lines 220 ₀,221 ₀, 222 ₀, 223 ₀ (of block 203 ₀) can include respective conductivematerials (a plurality of conductive materials) located along segmentsof pillars 331 and 332 and control lines 220 ₁, 221 ₁, 222 ₁, 223 ₁ (ofblock 203 ₁) can include respective conductive materials (a plurality ofconductive materials) located along segments of pillars 333 and 334.

Select line 281 _(A) (which includes a portion of select gate 261) canbe located in level 315 along a segment of pillar 331 (e.g., the segmentof pillar 331 on level 315). Select line 281 _(B) (which includes aportion of select gate 262) can be located in level 314 along a segmentof pillar 331 (e.g., the segment of pillar 331 on level 314). Selectline 281′ (which includes a portion of select gate 263) can be locatedin level 309 along a segment of pillar 331 (e.g., the segment of pillar331 on level 309).

In a similar structure, select lines 282 _(A), 283 _(A), and 284 _(A)can be located in level 315 along a segment (e.g., the segment in level315) of a respective pillar among pillars 332, 333, and 334. Selectlines 282 _(B), 283 _(B), and 284 _(A) can be located in level 314 alonga segment (e.g., the segment in level 314) of a respective pillar amongpillars 332, 333, and 334. Select lines 282′, 283′, and 284′ can belocated in level 309 along a segment (e.g., the segment in level 309) ofa respective pillar among pillars 332, 333, and 334.

The select lines on the same level (e.g., select lines 281 _(A), 282_(A), 283 _(A), and 284 _(A) on level 315) can have the same material.The select lines on different levels can have the same material ordifferent materials. The materials for the select lines of memory device200 can include conductively doped polycrystalline silicon (e.g., eithern-type or p-type), metals, or other conductive materials.

As shown in FIG. 2F, each of memory cells 210, 211, 212, and 213 of caninclude a structure 307, which includes portions 301, 302, and 303between a respective pillar and a control line. For example, memory cell213 of memory cell string 231 includes a structure 307 (which includesportions 301, 302, and 303) between pillar 331 and control line 203 ₀.Portion 301 can include a charge blocking material or materials (e.g., adielectric material such as silicon nitride) that is capable of blockinga tunneling of a charge. Portion 302 can include a charge storageelement (e.g., charge storage material or materials) that can provide acharge storage function to represent a value of information stored inmemory cell 210, 211, 212, or 213. For example, portion 302 can includepolycrystalline silicon, which can operate as a floating gate (e.g., tostore charge) in a memory cell (e.g., a memory cell 210, 211, 212, or213). In this example, each of memory cells 210, 211, 212, and 213 has afloating-gate memory cell structure. Alternatively, portion 302 caninclude a charge trapping material (e.g., silicon nitride) that canoperate to trap charge in a memory cell (e.g., a memory cell 210, 211,212, or 213). In this example, each of memory cells 210, 211, 212, and213 has a charge-trap memory cell structure. Portion 303 can include atunnel dielectric material or materials (e.g., an oxide of silicon) thatis capable of allowing tunneling of a charge (e.g., electrons). Forexample, portion 303 can allow tunneling of electrons from portion 344(e.g., conductive channel) to portion 302 during a write operation andtunneling of electrons from portion 302 to portion 344 during an eraseoperation of memory device 200.

In FIG. 2F, each of select gates 261 can include a structure 304 betweena respective select line and a respective pillar. For example, selectgate 261 of select circuit 241 includes structure 304 between selectline 281 _(A) and pillar 331.

Each of select gates 262 can include a structure 305 between arespective select line and a respective pillar. For example, select gate261 of select circuit 241 includes structure 305 between select line 281_(B) and pillar 331.

Each of select gates 263 can include a structure 306 between arespective select line and a respective pillar. For example, select gate263 of select circuit 241′ includes structure 306 between select line281′ and pillar 331.

Structures 304, 305, and 306 can be similar or the same material (ormaterials). For example, each of select gates 261, 262, and 263 can havea structure similar to a FET structure. An example of an FET includes ametal-oxide semiconductor (MOS) transistor. As is known to those skilledin the art, a FET usually includes a transistor gate, a channel, and agate oxide between the transistor gate and the channel and can be indirect contact with the transistor gate and the channel. A FET does nothave a charge storage element (e.g., a floating gate) that provides acharge storage function. Thus, each of structures 304, 305, and 306 maynot include a charge storage element that provides a charge storagefunction. Therefore, unlike memory cells 210, 211, 212, and 213, each ofselect gates 261, 262, and 263 may not include a charge storage elementthat provides a charge storage function. For example, each of structures304, 305, and 306 can include only a dielectric material for (e.g.,includes only an oxide of silicon without a charge storage element).

Thus, as described above, shown in FIG. 2F and FIG. 2G, a select line(e.g., select line 281 _(A), 282 _(A), 283 _(A), 284 _(A), 281 _(B), 282_(B), 283 _(B), and 284 _(B), 281′, 282′, 283′, and 284′) is a piece(e.g., a line) of conductive material. The conductive material can be apiece of polycrystalline silicon, silicide, metal, or any combination ofthese materials, or other conductive materials. As described above, aselect line can carry a signal (e.g., signal SGD_(A), SGD_(A), or SGS)but it does not operate like a switch (e.g., a transistor). A selectgate (e.g., select gate 262, 262, or 263) can include a portion of aselect line (e.g., a portion of the piece of the conductive materialthat formed the select line) and additional structures to perform afunction (e.g., function of a transistor). For example, in selectcircuit 241 in FIG. 2F, select gate 261 can include a portion of selectline 281 _(A) and a structure 304; and select gate 262 can include aportion of select line 281 _(B) and a structure 305.

FIG. 2H shows details of a portion of memory device 200 of FIG. 2Fincluding structures 304, 305, 306, and 307, according to someembodiments described herein. For simplicity, only structures 304, 305,306, and 307 and part of select line 281 _(A), select line 281 _(B), andselect line 281′, control line 223 ₀, memory cell 213, and select gates261, 262, and 263 of memory device are shown in FIG. 2H.

As shown in FIG. 2H, select line 281 _(A), select line 281 _(B), controlline 223 ₀, and select line 281′ can be located along segments 351, 352,353, and 354, respectively, of pillar 331. Pillar 331 includes asidewall (e.g., a vertical sidewall) 339. Sidewall 339 can be thesidewall of the conductive channel formed by portion 344.

Select line 281 _(A) includes a sidewall 381 _(A) (e.g., a verticalsidewall of the conductive material of select line 281 _(A)) facingsidewall 399 of pillar 331. Sidewall 381 _(A) can be located at adistance D1 from a portion of pillar 331. Distance D1 can be measuredstraight across structure 304 from sidewall 381 _(A) to a respectiveportion of sidewall 339 of pillar 331, such that distance D1 can be theshortest distance between sidewalls 381 _(A) and 339.

Select line 281 _(B) includes a sidewall 381 _(B) (e.g., a verticalsidewall of the conductive material of select line 281 _(B)) facingsidewall 399 of pillar 331. Sidewall 381 _(B) can be located at adistance D2 from a portion of pillar 331. Distance D2 can be measuredstraight across structure 305 from sidewall 381 _(B) to a respectiveportion of sidewall 339 of pillar 331, such that distance D2 can be theshortest distance between sidewalls 381 _(B) and 339.

Control line 223 ₀ includes a sidewall 323 (e.g., a vertical sidewall ofthe conductive material control line 223 ₀) facing sidewall 399 ofpillar 331. Sidewall 323 can be located at a distance D3 from a portionof pillar 331. Distance D3 can be measured straight across structure 307from sidewall 323 to a respective portion of sidewall 339 of pillar 331,such that distance D3 can be the shortest distance between sidewalls 323and 339.

Select line 281′ includes a sidewall 381′ (e.g., a vertical sidewall ofthe conductive material of select line 281′) facing sidewall 399 ofpillar 331. Sidewall 381′ can be located at a distance D4 from a portionof pillar 331. Distance D4 can be measured straight across structure 306from sidewall 381′ to a respective portion of sidewall 339 of pillar331, such that distance D4 can be the shortest distance betweensidewalls 381′ and 339.

Distances D1, D2, and D4 can be the same. For example, select lines 281_(A), 281 _(B), and 281′ can be formed to have a similar or the samestructure that may result in distances D1, D2, and D4 to be the sameamong each other. Each of select lines 281 _(A), 281 _(B), and 281′ andmemory cells 210, 211, 212, and 213 can be formed to have differentstructures. For example, as shown in FIG. 2H, memory cell 213 can beformed to include a charge storage element included in portion 302. Thismay cause distance D3 to be greater than each of distances D1, D2, andD4.

As shown in FIG. 2H, structure 304 can extend from sidewall 381 _(A) ofselect line 281 _(A) to sidewall 339 of pillar 331. Structure 305 canextend from sidewall 381 _(B) of select line 281 _(B) to sidewall 339 ofpillar 331. Structure 307 can extend from sidewall 323 control line 223₀ to sidewall 339 of pillar 331. Structure 306 can extend from sidewall381′ of select line 281′ to sidewall 339 of pillar 331.

As shown in FIG. 2H, select line 281 _(A), select line 281 _(B), controlline 223 ₀, and select line 281′ have thickness T1, T2, T3, and T4,respectively. Thickness T1, T2, T3, and T4 can be the same or different.For example, thickness T1, T2, and T4 can be the same but can bedifferent from (e.g., greater than) thickness T3.

The following description with reference to FIG. 2I through FIG. 2Mdescribes variations of memory device 200 including variations indistances between pillar 331 and respective sidewalls of select lines281 _(A), 281 _(B), 281′, control line 223 ₀, variations in structures304, 305, 306, and 307, and variations in at least some of thicknessesT1, T2, T3, and T4. For simplicity, structures 304, 305, 306, and 307 inFIG. 2I through FIG. 2M are shown in dashed lines and their descriptionare not described in detail.

FIG. 2I shows a variation of the portion of memory device 200 of FIG. 2Hincluding sidewall 381 located at distance D5 that is greater thandistance D2 of FIG. 2H, according to some embodiments described herein.As shown in FIG. 2I, since distance D5 is greater than distance D2 (FIG.2H), structure 305 in FIG. 2I can also be different from (e.g., widerthan) structure 305 of FIG. 2H. Structure 305 in FIG. 2I can alsoinclude materials different from the materials of structure 305 of FIG.2H. For example, structure 305 can include portions and materialssimilar to those of portions 301, 302, and 303 of structure 307 ofmemory cell 213. In this example, structure 305 in FIG. 2 may be formedwhen structure 307 of memory cell 213 is formed (formed concurrentlywith structure 307). Thus, in the variation of memory device 200 of FIG.2I, each of select gates 262 can have a memory cell-type structure likememory cell 213. The memory cell-type structure of select gate 262allows it to be electrically programmed in order to adjust the thresholdvoltage of select gate 262.

FIG. 2J shows a variation of the portion of memory device 200 of FIG. 2Iincluding sidewall 381 _(A) located at distance D6 that is greater thandistance D1 of FIG. 2I, according to some embodiments described herein.Structure 304 in FIG. 2J can include materials similar to those ofstructure 305. Structure 304 may be formed concurrently with structure305 or, alternatively, concurrently with both structures 305 and 307. Inthis example, structure 304 can include portions and materials similarto those of portions 301, 302, and 303 of structure 307 of FIG. 2H.Thus, in the variation of memory device 200 of FIG. 2J, each of selectgates 261 and 262 can have a memory cell-type structure like memory cell213. The memory cell-type structure of select gate 261 allows it to beelectrically programmed in order to adjust the threshold voltage ofselect gate 262.

FIG. 2K shows a variation of the portion of memory device 200 of FIG. 2Hincluding sidewall 381′ of select line 281′ located at distance D7 thatis greater than distance D4 of FIG. 2H, according to some embodimentsdescribed herein. As shown in FIG. 2K, since distance D7 is greater thandistance D4 (FIG. 2H), structure 306 in FIG. 2K can also be differentfrom (e.g., wider than) structure 306 of FIG. 2H. Structure 306 in FIG.2K can also include materials different from the materials of structure306 of FIG. 2H. For example, structure 306 can include portions andmaterials similar to those of portions 301, 302, and 303 of structure307 of memory cell 213. In this example, structure 306 may be formedwhen structure 307 of memory cell 213 is formed (formed concurrentlywith structure 307). Thus, in the variation of memory device 200 in FIG.2K, each of select gates 263 can have a memory cell-type structure likememory cell 213. Structure 306 with associated distance D7 can beincluded in any of the variations of memory device 200 shown in FIG. 2Hthrough FIG. 2J. For example, select line 281′ and structure 306 (andassociated distance D7) of FIG. 2K can replace select line 281′ andstructure 306 (and associated distance D4) of FIG. 2H, FIG. 2I, and FIG.2J.

FIG. 2L shows a variation of the portion of memory device 200 of FIG. 2Hincluding select line 281 _(A) having a thickness T1′ that is greaterthan each of thicknesses T1, T2, T3, and T4 of FIG. 2H, according tosome embodiments described herein. Distance D1′ in FIG. 2L can be thesame or different from distance D1 of FIG. 2H. As an example, distanceD1′ can be similar to (e.g., equal to) distance D1 and less thandistance D3 (FIG. 2H). Select line 281 _(A) having thickness T1′ (FIG.2L) can be included in any of the variations of memory device 200 shownin FIG. 2H through FIG. 2K. For example, select line 281 _(A) havingthickness T1′ can be replace select line 281 _(A) of FIG. 2H, FIG. 2I,and FIG. 2J.

The greater thickness of T1′ allows more process flexibility duringprocesses of forming portion 343. As described above, portions 343 and344 may include materials of different conductivity type. For example,portion 343 may include polycrystalline silicon of n-type. Portion 344may include polycrystalline silicon of p-type. As shown in FIG. 2H,portion 343 may contact (e.g., interface with) portion 344 a location(e.g., junction) 347 in segment 351 of pillar 331. By forming selectline 281 _(A) having thickness T1′ that is relatively greater than thethickness (e.g., T2) of another select line (e.g., select line 281 _(B)immediately next to select line 281 _(A)), the length (e.g., channellength) of portion 344 at segment 351 (which is proportional tothickness T1′) may also extended to be relatively greater than length ofportion 344 at segment 352. This greater length may compensate forprocess variation in forming portion 343. For example, a greater lengthmay allow forming an enough overlap (N+ junction overlap) betweenportion 343 and select line 281 _(A) without extending portion 343 toofar towards select line 281 _(A). Such an overlap may allow enoughgate-induced drain-leakage (GIDL) current to be generated during anerase operation and may keep any GIDL current to be at relatively lowamount during read and write operations. The size (value) of thicknessT1′ can depend on the amount of the overlap. As an example, thicknessT1′ can be up to 1.5 times thickness T2. In another example, thicknessT1′ can be between 1.5 times thickness T2 to 2 times thickness T2. Inanother example, thickness T1′ can be more than 2 times thickness T2.

FIG. 2M shows a variation of the portion of memory device 200 of FIG. 2Hincluding select line 281′ having a thickness T4′ that is greater thanthicknesses T1, T2, T3, and T4 of FIG. 2H, according to some embodimentsdescribed herein. Distance D4′ in FIG. 2L can be the same or differentfrom distance D4 of FIG. 2H. As an example, distance D4′ can be similarto (e.g., equal to) distance D4 and less than distance D3 (FIG. 3H).Select line 281′ having thickness T4′ (FIG. 2M) can be included in anyof the variations of memory device 200 shown in FIG. 2H, through FIG.2L. For example, select line 281′ having thickness T4′ can replaceselect line 281′ of in FIG. 2H through FIG. 2L.

As described above with reference to FIG. 2A through FIG. 2M, memorydevice 200 can include double select gates (e.g., double drain selectgates) and can be based on techniques shown in charts 200D and 200E. Thecombination of the double gates and the biasing techniques describedabove may allow memory device 200 to achieve improvements over someconventional memory devices during read, write, and erase operations.For example, some conventional memory devices may include only one SGDselect line between a memory cell string and a data line. In such aconventional memory device, during a read or write operation, a voltageof 0V may be provided to the SGD select line if it is associated with adeselected block. The relatively low voltage (e.g., 0V) used in aconventional memory device may cause a GIDL event to occur near thelocation between the data line and the SGD select line. It may alsoincrease the coupling capacitance between the data line and the SGDselect line. Further, during an erase operation in such a conventionalmemory device, relatively higher values of voltages are applied to thedata line and the SGD select line of a selected block. This may cause arelatively higher electric field stress to occur near the SGD selectline.

As is known to those skilled in the art. GIDL current (e.g., too muchGIDL current) may sometime be harmful for a read or write operation in ablock of a particular memory device. But GIDL current may sometimes beuseful during an erase operation in a block of the particular memorydevice. The structure of the memory device and the biasing techniquesdescribed herein may help reduce or suppress GIDL current (e.g., GIDLcurrent in a deselected block) during a read or write operation ofmemory device 200. It may also help generate (e.g., increasing) GIDLcurrent (e.g., GIDL current in a selected block) during an eraseoperation of memory device 200.

For example, as described above with reference to chart 200D (FIG. 2D)and chart 200E (FIG. 2E) select lines 283 _(A) and 284 _(A) in block 203₁ (e.g., deselected block) in FIG. 2F can be provided (e.g., applied)with voltages (e.g., V3 or V7) having a relatively higher value (e.g.,V3=0.5V>0V during a read operation, or V7=2.3V>0V during a writeoperation). This higher voltages value may reduce the effective couplingcapacitance between line 270 and each of select lines 283 _(A) and 284_(A)(FIG. 2F). This may also reduce or suppress GIDL current betweenline 270 and each of select lines 283 _(A) and 284 _(A) (e.g., reduceGIDL current near the location between structure 304 and portion 343)during a read or write operation.

Additionally, as described above with reference to chart 200D (FIG. 2D)and chart 200E (FIG. 2E), select lines 283 _(B) and 284 _(B) in block203 ₁ (e.g., deselected block) in FIG. 2F can be provided (e.g.,applied) with voltages (e.g., V4 and V8) having a relatively lower value(e.g., V4=0V<V3=0.5V during a read operation, or V8=0V<V7=2.3V during awrite operation). This lower voltage value may reduce subthresholdleakage current that may occur at the location near select lines 283_(B) and 284 _(B).

Further, as described above with reference to chart 200D (FIG. 2D) andchart 200E (FIG. 2E), select lines 281 _(A) and 282 _(A) in block 203 ₀(selected block) can be provided (e.g., applied) with voltages having avalue of V9=10V. Since the value of the voltage provided to signal BL(associated with line 270) is 20V, the value of 10V may be sufficient togenerate (e.g., to cause) enough GIDL to assist with the erase operationperformed on block 203 ₀. As mention above with reference to thedescription of chart 200D (FIG. 2D), the values of the voltages shown inchart 200D are example values. Thus, the value of voltage V9 may beselected to be an alternative value different from 10V (e.g., selectedbased on the value of the voltage provide to signal BL in chart 200D) aslong as such an alternative value can result in enough GIDL beinggenerated during an erase operation of a selected block of memory device200.

Moreover, as described above with reference to chart 200D (FIG. 2D) andchart 200E (FIG. 2E), select lines 281 _(B) and 282 _(B) in block 203 ₀(selected block) can be provided (e.g., applied) with voltages having avalue of V10=14V during an erase operation. Since the value of thevoltage provided to signal BL (associated with line 270) is 20V, thevalue of 14V can help reduce an electric field stress that may occurnear select line 281 _(B) (e.g., at a location between select line 281_(B) and pillar 331) and near select line 282 _(B) (e.g., at a locationbetween select line 282 _(B) and pillar 332) during an erase operationperformed on block 203 ₀. As also described above, select lines 281 _(B)and 282 _(B) in block 203 ₀ (selected block) can alternatively beprovided with voltages having a value of V10=10V. This voltage value maybe sufficient (e.g., relative to 5V provided to control line 220 ₀) tohelp reduce an electric field stress that may occur near select line 281_(B) (e.g., at a location between select line 281 _(B) and control line220 ₀) during an erase operation performed on block 203 ₀.

Thus, as described above with reference to FIG. 2A through FIG. 2M, thestructure of memory device 200 and the biasing techniques (e.g., basedon chart 200E of FIG. 2D and chart 200E of FIG. 2E) described herein mayhelp reduce or suppress GIDL current in a block (e.g., selected block,deselected block, or both) during a read or write operation of memorydevice 200. The structure of memory device 200 and the biasingtechniques described herein may also help provide enough GIDL currentduring an erase operation performed on a block of memory device 200.

FIG. 3A shows a block diagram of a portion of a memory device 300, whichcan be a variation of memory device 200, according to some embodimentsdescribed herein. Memory device 300 includes elements similar to oridentical to those of memory device 200. For simplicity, the descriptionof similar or identical elements (which have the same labels in FIG. 2Aand FIG. 3A) between memory devices 200 and 300 is not repeated in thedescription of FIG. 3A.

As shown in FIG. 3A, memory device 300 can include double (e.g., upperand lower) source select lines, including select lines 281′_(A),282′_(A), 283′_(A), and 284′_(A) (e.g., upper source select lines) andselect lines 281′_(B), 282′_(B), 283′_(B), and 284′_(B). This differentfrom memory device 200 of FIG. 2A where memory device 200 has only onesource select line (e.g., 281′, 282′, 283′, and 284′) associated witheach of select circuits 241′ through 252′. In FIG. 3A, select lines281′_(A), 282′_(A), 283′_(A), and 284′_(A) can correspond to selectlines 281′, 282′, 283′, and 284′ of FIG. 2A.

In memory device 300 of FIG. 3A, each of select lines 281′_(A),282′_(A). 283′_(A), and 284′_(A) can carry a separate (e.g., different)signal SGS_(A). Each of select lines 281′_(B), 282′_(B), 283′_(B), and284′_(B) can carry a separate (e.g., different) signal SGS_(B). Each ofselect circuits 241′ through 252′ can share two select lines. Forexample, select circuits 241′. 243′, and 245′ can share select lines281′_(A) and 281′_(B). Select circuits 242′, 244′, and 246′ can shareselect lines 282′_(A) and 282 _(B). Select circuits 243′, 249′, and 251′can share select lines 283′_(A) and 283′_(B). Select circuits 248′,250′, and 252′ can share select lines 284′_(A) and 284′_(B). FIG. 3Ashows select line 281 _(A) being coupled to select lines 282 _(A) andselect line 283 _(A) being coupled to select lines 242A. However,similar to memory device 200 of FIG. 2A, select lines 281 _(A) and 282_(A) can be uncoupled from each other, and select lines 283 _(A) and 284_(A) can be uncoupled from each other.

FIG. 3B shows schematic diagram of memory device 300 of FIG. 3A,according to some embodiments described herein. Memory device 300includes elements similar to or identical to those of memory device 200of FIG. 2B. For simplicity, the description of similar or identicalelements (which have the same labels in FIG. 2B and FIG. 3B) betweenmemory devices 200 and 300 is not repeated in the description of FIG.3A.

As shown in FIG. 3B, each of select circuits 241′ through 252′ caninclude double select gates (e.g., double source select gates): one ofselect gates 263 and one of select gates 264. Similar to each of selectgates 263, each of select gates 264 can also operate as a transistor(e.g., a FET).

FIG. 3B shows an example where signal SGS_(A) associated with selectline 281′_(A) and signal SGS_(A) associated with select line 282′_(A)are separate signals, and signal SGS_(A) associated with select line283′_(A) and signal SGS_(A) associated with select line 284′_(A) areseparate signals. In a variation of memory device 300, signal SGS_(A)associated with select line 281′_(A) and signal SGS_(A) associated withselect line 282′_(A) can be a shared signal (e.g., can be the samesignal); and signal SGS_(A) associated with select line 283′_(A) andsignal SGS_(A) associated with select line 284′_(A) can be a sharedsignal (e.g., can be the same signal).

FIG. 3B shows an example where signal SGS_(B) associated with selectline 281′_(B) and signal SGS_(B) associated with select line 282′_(B)are separate signals, and signal SGS_(B) associated with select line283′_(B) and signal SGS_(B) associated with select line 284′_(B) areseparate signals. In a variation of memory device 300, signal SGS_(B)associated with select line 281′_(B) and signal SGS_(B) associated withselect line 282′_(B) can be a shared signal; and signal SGS_(B)associated with select line 283′_(B) and signal SGS_(B) associated withselect line 284′_(B) can be a shared signal.

FIG. 3C shows a schematic diagram of a portion of memory device 300 ofFIG. 3B including memory cell strings 231, 232, 237, and 238 and selectcircuits 241, 242, 247, 248, 241′, 242′, 247′, and 248′ coupled betweenline 270 and line 299, according to some embodiments described herein.Portion of memory device 300 shown in FIG. 3C includes elements similarto or identical to those of memory device 200 of FIG. 2C. Forsimplicity, the description of similar or identical elements betweenmemory devices 200 and 300 is not repeated in the description of FIG.3C.

As shown in FIG. 3C, select gates (e.g., double source select gates) 263and 264 each of select circuits 241′, 242′. 247′, and 248′ can becoupled in series between line 299 and a respective memory cell stringamong memory cell strings 231, 232, 237, and 238. Select gate 263 ofselect circuit 241′ has a terminal (e.g., a transistor gate) that can bepart of (e.g., formed by a portion of) select line 281′_(A). Select gate264 of select circuit 241′ has a terminal (e.g., a transistor gate) thatcan be part of (e.g., formed by a portion of) select line 281′. Selectgates 263 and 264 of select circuit 241′ can be controlled (e.g., turnedon or turned off) by signals SGS_(A) and SGS_(B) provided to selectlines 281′_(A) and 281′, respectively. Similarly, as shown in FIG. 3C,select gates 263 and 264 of each of select circuits 242, 247, and 248also have terminals (transistor gates) that can be parts of (e.g.,formed by portions of) respective select lines among select lines282′_(A), 283′_(A). 284′_(A), 282's, 283′_(B), and 284′_(B).

FIG. 3D is a chart 300D showing example values of voltages provided tosignals BL, SGD_(A), SGD_(B), WL selected, WL unselected, SGS_(A),SGS_(B), and SRC of memory device 300 during read, write, and eraseoperations of memory device 300, according to some embodiments describedherein. Differences between chart 300D and chart 200D (FIG. 2D) includethe values of voltages provided to signals SGS_(A) and SGS_(B) duringread, write, and erase operations of memory device 300. Other signalsshown in chart 300D FIG. 3D can be provided with voltages having valuessimilar to or identical to those of chart 200D of FIG. 2D. The followingdescription of FIG. 3D uses the same assumptions (e.g., selected anddeselected blocks and strings) used in description of FIG. 2D.

During a read operation of memory device 300 (FIG. 3C), for a selectedblock (e.g., block 203 ₀), signals SGS_(A) and SGS_(B) in FIG. 3Dassociated with a selected string of the selected block can be provided(e.g., bias) with voltages having the same value, such asSGS_(A)=SGS_(B)=5V. Thus, in this example, select lines 281′_(A) and281′_(B) (FIG. 3C) associated with memory cell string 231 (e.g.,selected string) can be provided with voltages having the same value of5V. Hence, select gates 263 and 264 of select circuit 241′ can receivevoltages having the same value of 5V. Signals SGS_(A) and SGS_(B)associated with a deselected string of the selected block can beprovided with voltages having the same value, such asSGS_(A)=SGS_(B)=0V. Thus, in this example, select lines 282′_(A) and282′_(B) associated with memory cell string 232 (e.g., deselectedstring) can be provided with voltages having the same value of 0V.Hence, select gates 263 and 264 of select circuit 242′ can receivevoltages having the same value of 0V.

During a read operation of memory device 200 (FIG. 3C) for a deselectedblock (e.g., block 203), signals SGS_(A) and SGS_(B) associated with allstrings (e.g., strings 237 and 238) of the deselected block can beprovided (e.g., bias) with voltages having the same, such asSGS_(A)=SGS_(B)=0V. Thus, in this example, in block 203 ₁ (deselectedblock), select lines 283 _(A) and 284 _(A) can be provided with voltageshaving the same value of 0V; and select lines 283 _(B) and 284 _(B) canbe provided with voltages having values of 0V. Hence, select gates 263and 264 of select circuits 247 and 248 can receive voltages having thesame value of 0V; and select gates 262 of select circuits 247′ and 248′can receive voltages having the same value of 0V.

During a write operation of memory device 200 (FIG. 3C) for a selectedblock (e.g., block 203 ₀), signals SGS_(A) and SGS_(B) associated with aselected string can be provided (e.g., bias) with voltages havingdifferent values, such as SGS_(A)=V13=2.3V and SGS_(B)=V14=0V. Thus, inthis example, select lines 281 _(A) and 281 _(B) (FIG. 3C) associatedwith memory cell string 231 (selected string) can be provided withvoltages having values of 2.3V and 0V, respectively. Hence, select gates263 and 264 of select circuit 241 can receive voltages of 2.3V and 0V,respectively. Signals SGS_(A) and SGS_(B) associated with a deselectedstring can be provided with voltages having different values, such asSGS_(A)=V15=2.3V and SGS_(B)=V16=0V. Thus, in this example, select lines282 _(A) and 282 _(B) associated with memory cell string 232 (deselectedstring) can be provided with voltages having values of 2.3V and 0V,respectively. Hence, select gates 263 and 264 of select circuit 242′ canreceive voltages having values of 2.3V and 0V, respectively.

During a write operation of memory device 200 (FIG. 3C) for a deselectedblock (e.g., block 203 ₁), signals SGS_(A) and SGS_(B) associated withall strings of block 203 ₁ can be provided (e.g., bias) with voltageshaving different values, such as SGS_(A)=V17=2.3V and SGS_(B)=V18=0V.Thus, in this example in, block 203 ₁ (deselected block), select lines283 _(A) and 284 _(A) can be provided with voltages having values of2.3V; and select lines 283 _(B) and 284E can be provided with voltageshaving values of 0V. Hence, each of select gates 263 of select circuits247′ and 248′ can receive a voltage having a value of 2.3V: each ofselect gates 264 of select circuits 247′ and 248′ can receive a voltagehaving a value of 0V.

During an erase operation of memory device 200 (FIG. 3C) for a selectedblock, based on the above assumptions and as shown in chart 300D of FIG.3D, signals SGS_(A) and SGS_(B) associated with a selected string and adeselected string can be provided with voltages having different values,such as SGS_(A)=V19=15V and SGS_(B)=V20=11V. Thus, in this example, inblock 203 ₀, select lines 281 _(A) and 282 _(A) (FIG. 3C) can beprovided with voltages having values of 15V; and select lines 281 _(B)and 282 _(B) can be provided with voltages having values of 11V. Hence,select gates 263 of select circuits 241′ and 242′ can receive voltageshaving values of 15V: select gates 264 of select circuits 241′ and 242′can receive voltages having values of 11V.

During an erase operation of memory device 300 (FIG. 3C) for adeselected block, select lines 283 _(A) and 283E (FIG. 3C) of block 203₁ (deselected block) may be placed in a “float” state (shown as “F” inFIG. 3D). In the float state, the voltages on select lines 283′_(A),283′_(B), 284′_(A), and 284 _(B) may have values proportional to thevalue (e.g., approximately 20V) of the voltage provided to signal BL(e.g., signal BL0 in this example). Hence, select gates 263 and 264 ofselect circuits 247′ and 248′ of block 203 ₁ (deselected block) can beplaced in the float state in an erase operation.

FIG. 3E is a chart 300E showing example values of voltages provided tosignals BL, SGD_(A), SGD_(B), WL selected, WL unselected, SGS, and SRCof memory device 200 during read, write, and erase operations of memorydevice 300 when signal SGD_(A) associated with select line 281 _(A) andsignal SGD_(A) associated with select line 282 _(A) can be separatesignals (e.g., not a shared signal) in a variation of memory device 300,according to some embodiments described herein. Chart 300E can be avariation of chart 300D where signals SGD_(A) and SGDs are separatesignals. Thus, in chart 300E, voltages of different values can beprovided to signals SGD_(A) associated with select line 281 _(A) andsignal SGD_(A) associated with select line 282 _(A) of a deselectedstring of a selected block. The values of voltages provided to signalsin chart 300E can be the same as those in chart 200E of FIG. 2E.

Providing (e.g., applying) voltages to signals SGD_(A), SGD_(A), SGS_(A)and SGS_(A) as shown in chart 300E may allow memory device 300 toachieve improvements at least similar to (e.g., better than) theimprovements provided by memory device 200, as described above withreference to FIG. 2A through FIG. 2E. For example, the structure ofmemory device 300 and the biasing (e.g., based on chart 300E of FIG. 3E)techniques described herein may help reduce or suppress GIDL current ina block (e.g., in a deselected block and in a portion associated withdeselected strings of a selected block) during a read or write operationof memory device 300. In another example, the structure of memory device300 and the biasing techniques described herein may also help provideenough GIDL current and reduce electric field stress during an eraseoperation performed on a block of memory device 300.

FIG. 3F shows a side view of a structure of a portion of memory device300, according to some embodiments described herein. The structure ofmemory device 300 in FIG. 3E corresponds to the schematic diagram ofmemory device 300 shown in FIG. 3C. The structure of memory device 300in FIG. 3E can be a variation of the structure of memory device 200 ofFIG. 2F. For simplicity, the description of similar or identicalelements (which have the same labels in FIG. 2F and FIG. 3F) betweenmemory devices 200 and 300 is not repeated in the description of FIG.3F. FIG. 3G shows a top view of a structure of a portion of memorydevice 300 of FIG. 3F, according to some embodiments described herein.Differences between memory device 300 of FIG. 3F and memory device 200(FIG. 2F) include, as shown in FIG. 3F, the double select lines (e.g.,select lines 281′_(A), 282′_(A), 283′_(A), and 284′_(A) and select lines281′_(B), 282′_(B), 283′_(B), and 284′_(B)) between substrate 390 and arespective memory cell string.

Select lines 281′_(A), 282′_(A), 283′_(A), and 284′_(A) can have any ofthe variations (e.g., material, distance from its sidewall to therespective pillar, and thickness) of select line 281′ described abovewith reference to FIG. 2A through FIG. 2M. Select lines 281′_(B),282′_(B), 283′_(B), and 284′_(B) can have any of the variations (e.g.,material, distance from its sidewall to the respective pillar, andthickness) of select line 281′ described above with reference to FIG. 2Athrough FIG. 2M.

Memory device 300 can include improvements at least similar to those ofmemory device 200. For example, the structure of memory device 300 andthe biasing techniques (e.g., based on chart 300D of FIG. 3D and chart300E of FIG. 3E) described herein may help reduce or suppress GIDLcurrent in a block (e.g., selected block, deselected block, or both)during a read or write operation of memory device 200 and providingenough GIDL current during an erase operation performed on a selectedblock of memory device 300.

FIG. 4A and FIG. 4B show a schematic diagram and a structure,respectively, of a portion a memory device 400 including triple drainselect lines and associated drain select transistors and triple sourceselect lines and associated source select transistors, according to someembodiments described herein. Memory device 400 can be a variation ofmemory device 300. For simplicity, only a portion of memory device 400is shown in FIG. 4A and FIG. 4B. The description of similar or identicalelements (which have the same labels in FIG. 3B, FIG. 4A, and FIG. 4B)between memory device 300 and 400 is not repeated in the description ofFIG. 4A and FIG. 4B. Differences between memory devices 300 and 400include, as shown in FIG. 4A and FIG. 4B, an addition of select lines281 _(C) and 282 _(C), select gates 266, and a signal SGD_(C) associatedwith each of select lines 281 _(C) and 282 _(C), and an addition ofselect lines 281′_(C) and 282′_(C), select gates 265, an a signalSGS_(C) associated in each of select lines 281′_(C) and 282′_(C). Asshown in FIG. 4A, select lines 281′_(A) and 282′_(A) can be connected toeach other by a connection 281′″_(A) (which can be a direct or indirectconnection similar to connection 281″_(A) in FIG. 2A). In FIG. 4A,memory device 400 can include variations of memory devices 200 and 300described above with reference to FIG. 2A through FIG. 3G.

During an operation (e.g., read, write, or erase operation) of memorydevice 400, signals SGD_(B) and SGD c can be provided with the samevoltages as those provided to signal SGD in chart 300D (FIG. 3D) orchart 300E (FIG. 3E), and signals SGS_(B) and SGS c can be provided withthe same voltages as those provided to signal SGS$ in chart 300D (FIG.3D) or chart 300E (FIG. 3E), Including triple select lines (e.g., drainselect lines) 281 _(A), 281 _(B), and 281 _(C), and triple select lines(e.g., source select lines) 281′_(A), 281′_(B), and 281′_(C) may allowmemory device 400 to achieve similar improvements as memory device 200or memory device 300 described above with reference to FIG. 2A throughFIG. 3G.

FIG. 5A through FIG. 24 show processes of forming memory devices,according to some embodiments described herein. The processes describedwith reference to FIG. 5A through FIG. 24 can be used to form memorydevices including memory devices 200, 300, and 400 and their variations.Some of the processes of forming memory devices and some of the elementsof memory device, such as the memory devices shown in FIG. 5A throughFIG. 24, may be readily known to those skilled in the art. Thus, to helpfocus on the embodiments described herein, some of the processes offorming the memory devices shown FIG. 5A through FIG. 24 and additionalprocesses to complete those memory devices are omitted. Further, forsimplicity, similar or identical elements among in FIG. 2 through FIG.4B and FIG. 5A through FIG. 24 are given the same labels.

FIG. 5A and FIG. 5B show processes of forming a memory device 500,according to some embodiments described herein. FIG. 5A shows memorydevice 500 after select lines 281 _(A), 281 _(B), 281′_(A), 281′_(B),282 _(A), 282 _(B), 282′_(A), and 282′_(B), and control lines 220 ₀, 221₀, 222 ₀, and 223 ₀ are formed, such as by depositing alternatingdielectric materials between the conductive materials (e.g., layers) ofselect lines 281 _(A), 281 _(B), 281′_(A), 281′_(B), 282 _(A), 282 _(B),282′_(A), and 282′_(B), and control lines 220 ₀, 221 ₁, 222 ₀, and 223₀. Then, pillar holes 521 and 522 can be formed in the alternatingconductive materials and the dielectric materials. In FIG. 5A, label “N”refers to conductive material of n-type (e.g., conductively dopedpolycrystalline silicon of n-type) that can be included in select lines281 _(A), 281 _(B), 281′_(A), 281′_(B), 282 _(A). 282 _(B), 282′_(A),and 282′_(B), and control lines 220 ₀, 221 ₀, 222 ₀, and 223 ₀. Then-type materials are used as an example. Other conductive materials(e.g., p-type materials, metals, and other conductive materials) can beused. FIG. 5B shows memory device 500 after memory cell strings 231 and232 and select gates 261, 262, 263, and 264 are formed. Portion 344(e.g., conductive channel) and portion 345 (e.g., dielectric filler) canbe formed in each of pillar holes 521 and 522 after memory cell strings231 and 232 and select gates 261, 262, 263, and 264 are formed. Pillarholes 521 and 522 including respective portions 344 and 345 are parts ofpillars (pillars of materials) 531 and 532, respectively.

As shown in FIG. 5B, each of select gates 261, 262, 263, and 264 can beformed such that it can have a memory cell-type structure, which issimilar or an identical structure of each of the memory cells of memorycell strings 231 and 232. The memory cell-type structure of each ofselect gates 261, 262, 263, and 264 may simplify fabrication process. Itmay also allow electrical programming of select gates 261, 262, 263, and264 in order to adjust the threshold voltages of select gates 261, 262,263, and 264. This may improve biasing of select lines 281 _(A), 281_(B), 281′_(A), 281′_(B), 282 _(A), 282 _(B), 282′_(A), and 282′_(B)during operations of memory device 500. Further, since each of selectgates 261 and 263 have a memory cell-type structure, select gates 261and 263 may not be susceptible to degradation from GIDL erase techniquesused in memory device 500.

FIG. 6A and FIG. 6B show processes of forming a memory device 600,according to some embodiments described herein. Similar to memory device500 (FIG. 5A and FIG. 5B), FIG. 6A shows memory device 600 after selectlines 281 _(A), 281 _(B), 281′_(A), 281′_(B), 282 _(A), 282 _(B),282′_(A), and 282′_(B), and control lines 220 ₀, 221 ₀, 222 ₀, and 223₀, and pillar holes 521 and 522 are formed. In FIG. 6A, label “P” refersto conductive material of p-type (e.g., conductivelydoped-polycrystalline silicon of p-type). Select line 281 _(A), 282_(A), 281′_(A), and 282′_(A) can include conductive material of p-type.FIG. 6B shows memory device 600 after memory cell strings 231 and 232,select gates 261, 262, 263, and 264. Pillars (pillars of materials) 631and 632 are also formed. Each of pillars 831 and 832 can includematerials of respective portions 344 and 345. Similar to memory device500 (FIG. 5B), each of select gates 262 and 264 of memory device 600 canbe formed such that it can have a memory cell-type structure. Unlikeselect gates 261 and 263 of memory device 500, each of select gates 261and 263 of memory device 600 can be formed such that it can have aFET-type structure. The memory cell-type structure of each of selectgates 262 and 264 may allow electrical programming of select gates 262and 264 in order to adjust the threshold voltages of select gates 262and 264. This may improve biasing of select lines 281 _(B), 281′_(B),282 _(B), and 282′_(B) during operations of memory device 600.

FIG. 7A and FIG. 7B show processes of forming a memory device 700,according to some embodiments described herein. The processes of formingmemory device 700 are similar to those used to form memory device 600 ofFIG. 6B. In memory device 700, however, each of select gates 261, 262,263, and 264 can be formed such that it can have a FET-type structure.This structure may help maintain the relative size of memory device 700(e.g., allowing chip size to remain unchanged).

FIG. 8A through FIG. 8D show processes of forming a memory device 800including forming multiple pillar holes at different times, according tosome embodiments described herein. FIG. 8A shows memory device 800 afterselect lines 281 _(B), 281′_(A), 281′_(B), 282 _(B), 282′_(A), and282′_(B), and control lines 220 ₀, 221 ₀, 222 ₀, and 223 ₀ are formed.Pillar holes 821 and 822 can be formed after select lines 281 _(B),281′_(A), 28′_(B), 282 _(B), 282′_(A), and 282′_(B), and control lines220 ₀, 221 ₀, 222 ₀, and 223 ₀ are formed.

FIG. 8B shows memory device 800 after memory cell strings 231 and 232and select gates 262, 263, and 264 are formed. Portion 344 and portion345′ (e.g., dielectric filler) can be formed in each of pillar holes 821and 822 after memory cell strings 231 and 232 and select gates 262, 263,and 264 are formed. As shown in FIG. 8B, each of select gates 262 and264 can be formed such that it can have a memory cell-type structure.Each of select gates 263 can be formed such that it can have a FET-typestructure.

FIG. 8C shows memory device 800 after select lines 281 _(A) and 282 _(A)are formed. Pillar holes 821′ and 822′ can be formed after select lines281 and 282 a are formed.

FIG. 8D shows memory device 800 after select gates 261 are formed. Eachof select gates 261 can be formed such that it can have a FET-typestructure. Portions 343 and 345 can be formed after select gates 261 areformed. Portions 343, 344, and 345 are parts of a respective pillar,such as pillar 831 or 832.

FIG. 9A through FIG. 9D show processes of forming a memory device 900including forming multiple pillar holes at different times, according tosome embodiments described herein. FIG. 9A shows memory device 900 afterselect lines 281′_(A), 281′_(B), 282′_(A), 282′_(B), and control lines220 ₀, 221 ₀, 222 ₀, and 223 ₀ are formed. Pillar holes 921 and 922 canbe formed after select lines 281′_(A), and 281′_(B), and control lines220 ₀, 221 ₀, 222 ₀, and 223 ₀ are formed.

FIG. 9B shows memory device 900 after memory cell strings 231 and 232and select gates 263 and 264 are formed. Portion 344 and portion 345′(e.g., dielectric filler) can be formed in each of pillar holes 921 and922 after memory cell strings 231 and 232 and select gates 263 and 264are formed. As shown in FIG. 9B, each of select gates 263 and 264 can beformed such that it can have a FET-type structure.

FIG. 9C shows memory device 900 after select lines 281 _(A), 282 _(A),281 _(B), and 282 _(B) are formed. Then, pillar holes 921′ and 922′ canbe formed. FIG. 9D shows memory device 900 after select gates 261 and262 are formed. Each of select gates 261 and 262 can be formed such thatit can have a FET-type structure. Portions 343 and 345 can be formedafter select gates 261 and 262 are formed. The materials of portions343, 344, and 345 are parts of the materials of a respective pillar,such as pillar 931 or 932.

FIG. 10A through FIG. 10D show processes of forming a memory device 1000including triple silicide drain select lines, according to someembodiments described herein. FIG. 10A shows memory device 1000 afterselect lines 281′_(A), 281′_(B), 281′_(C), 282′_(A), 282′_(B), and282′_(C), select gates 263, 264, and 265, control lines 220 ₀, 221 ₀,222 ₀, and 223 ₀, memory cell strings 231 and 232, structures (e.g.,layers of n-type materials) 280, and pillars 1031 and 1032 are formed.Each of select gates 263, 264, and 265 can be formed such that it canhave a FET-type structure. Portion 344 (e.g., conductive channel) andportion 345 (e.g., dielectric filler) can be also formed. Portions 344and 345 are parts of a respective pillar, such as pillar 1031 or 1032.

FIG. 10B shows memory device 1000 after openings (e.g., slits or cuts)1080 are formed (e.g., by etching portions of structures 280 at openings1080), resulting in the formation of select lines 281 _(A), 281 _(B),281 _(C), 282 _(A), 282 _(B), 282 _(C) and select gates 261, 262, and266. Then, material 1081 can be formed (e.g., by deposition) in openings1080. Material 1081 can include cobalt, nickel, or other conductivematerials. As shown in FIG. 10B, select lines 281 _(A), 281 _(B), 281_(C) can include n-type material (e.g., n-type polycrystalline silicon).

FIG. 10C shows memory device 1000 after a silicidation process isperformed and after materials 1081 are removed from openings 1080. Thesilicidation process causes the material (e.g., n-type polycrystallinesilicon) of select lines 281 _(A), 281 _(B), 281 _(C), 282 _(A), 282_(B), 282 _(C) to become silicide materials (e.g., NiSi, CoSi. or othersilicide materials).

FIG. 10D shows memory device 1000 after dielectric materials (e.g., anoxide of silicon) are formed in openings 1080 (FIG. 10C). Providingselect lines 281 _(A), 281 _(B), 281 _(C), 282 _(A), 282 _(B), and 282_(C) with silicide materials may reduce the resistance of these selectlines.

FIG. 11A through FIG. 11F show processes of forming a memory device 1100including triple metal drain select lines, according to some embodimentsdescribed herein. Similar to memory device 1000 of FIG. 10A, FIG. 1Ashows memory device 1100 after select lines 281′_(A), 281′_(B),281′_(C), 282′_(A), 282′_(B), and 282′_(C), select gates 263, 264, and265, control lines 220 ₀, 221 ₀, and 222 ₀, and 223 ₀, memory cellstrings 231 and 232, pillar holes 1131 and 1132, and structures (e.g.,layers of materials) 280 are formed. FIG. 1A shows structures 280including n-type material (e.g., n-type polycrystalline silicon) as anexample. Structures 280 can include silicon nitride. Portion 344 (e.g.,conductive channel) and portion 345 (e.g., dielectric filler) can alsobe formed. Portions 344 and 345 are parts of a respective pillar, suchas pillar 1131 or 1132.

FIG. 11B shows memory device 1100 after openings 1180 are formed (e.g.,by etching portions of structures 280 at openings 1180). This results inthe formation of select lines 281 _(A), 281 _(B), 281 _(C), 282 _(A),282 ^(B), and 282 _(C) and select gates 261, 262, and 266.

FIG. 11C shows memory device 1100 after the materials of select lines281 _(A), 281 _(B), and 281 _(C) are removed. This creates voids at thelocations where the materials of select lines 281 _(A), 281 _(B), and281 _(C) were.

FIG. 11D shows memory device 1100 after materials 1181 fill (e.g., bydeposition) the voids at the locations where the materials of selectlines 281 _(A). 281 _(B), 281 _(C), 282 _(A), 282 _(B), and 282 _(C)were removed (FIG. 1C). Materials 1181 can include metals or otherconductive materials (e.g., W, Ti, Ta, WN, TiN, TaN, or other conductivematerials).

FIG. 11E shows memory device 1100 after openings 1182 are formed (e.g.,by etching portions of materials 1181 at openings 1182). A portion ofmaterials 1181 were removed at opening 1182. The remaining portion ofmaterials is included in select lines 281 _(A), 281 _(B), 281 _(C), 282_(A), 282 _(B), and 282 _(C).

FIG. 11F shows memory device 1100 after dielectric materials (e.g., anoxide of silicon) are formed in openings 1182 (FIG. 11E). Providingselect lines 281 _(A), 281 _(B), 281 _(C), 282 _(A), 282 _(B), and 282_(C) with materials 1181 (e.g., metals) may reduce the resistance ofthese select lines.

FIG. 12A and FIG. 12B show processes of forming a memory device 1200including triple source select transistors having a combination ofmemory cell-type and FET-type structures, according to some embodimentsdescribed herein. FIG. 12A shows memory device 1200 after select lines281′_(A), 281′_(B), 218′_(C), 282′_(A), 282′_(B), and 282′_(C), controllines 220 ₀, 221 ₀, 222 ₀, and 223 ₀, and pillar holes 1231 and 1232 areformed. FIG. 12B shows memory device 1200 after memory cell strings 231and 232 and select gates 263, 264, and 265 are formed. Portion 346(e.g., N+ material), portion 344 (e.g., conductive channel), and portion345 (e.g., dielectric filler) can be formed in each of pillar holes 1221and 1222. Portions 344 and 345 are parts of a respective pillar, such aspillar 1231 or 1232. As shown in FIG. 12B, the thickness of select lines281′_(A) and 282′_(A) can be greater than the thickness of select lines281′_(B), 218′_(C), 282′, and 282′_(C).

Each of select gates 264 and 265 can be formed such that it can have amemory cell-type structure, which is similar or an identical structureof each of the memory cells of memory cell strings 231 and 232. Each ofselect gates 263 can be formed such that it can have a FET-typestructure. Other parts of memory device 1200 (e.g., SGD select lines andassociated transistors (e.g., 261, 262 and 263)) can be formed byprocesses similar to any of the processes described about with referenceto FIG. 5A through FIG. 11F. The combination of memory cell-type andFET-type structures of select gates 263, 264, and 265 shown in FIG. 12Bmay allow select lines 281′_(B), 282′_(B), 281 _(C), and 282′_(C) to berelatively thin. It may also make process path easier.

FIG. 13A and FIG. 13B show processes of forming a memory device 1300including triple source select transistors having a combination ofmemory cell-type and FET-type structures, according to some embodimentsdescribed herein. FIG. 13A shows memory device 1300 after formation ofelements similar to memory device 1200 of FIG. 12A. As shown in FIG.13B, however, each of select gates 264 and 265 can be formed such thatit can have a FET-type structure. Each of select gates 263 can be formedsuch that it can have a memory cell-type structure, which is similar oran identical structure of each of the memory cells of memory cellstrings 231 and 232. Other parts of memory device 1300 (e.g., SGD selectlines and associated transistors (e.g., 261, 262 and 263) can be formedby processes similar to any of the processes described above withreference to FIG. 5A through FIG. 11F. The combination of memorycell-type and FET-type structures of select gates 263, 264, and 265shown in FIG. 13B may reduce the resistance of select lines 281′_(A) and282′_(A).

FIG. 14A and FIG. 14B show processes of forming a memory device 1400including triple source select transistors having a combination ofmemory cell-type and FET-type structures, according to some embodimentsdescribed herein. FIG. 14A shows memory device 1400 after formation ofelements similar to memory device 1200 of FIG. 12A. As shown in FIG.14B, however, each of select gates 263, 264, and 265 can be formed suchthat it can be a memory cell-type structure, which is similar or anidentical structure of each of the memory cells of memory cell strings231 and 232. Other parts of memory device 1400 (e.g., SGD select linesand associated transistors (e.g., 261.262 and 263) can be formed byprocesses similar to any of the processes described about with referenceto FIG. 5A through FIG. 11F. The combination of memory cell-type andFET-type structures of select gates 263, 264, and 265 shown in FIG. 14Bmay reduce the resistance of select lines 281′_(A) and 282′a.

FIG. 15 shows a memory device 1500 including triple drain selecttransistors and triple source select transistors, according to someembodiments described herein. Memory device 1500 can be formed using anycombination of the processes described about with reference to FIG. 5Athrough FIG. 14B. As shown in FIG. 15, memory device 1500 can includeelements similar to or identical to the elements of the memory devicesdescribed above (FIG. 2A through FIG. 14B). Thus, for simplicity, thedescription of the elements of memory device 1500 is not described here.As shown in FIG. 15, each of select gates 265 and 266 can be formed suchthat it can have a memory cell-type structure, which is similar or anidentical structure of each of the memory cells of memory cell strings231 and 232. Each of select gates 261, 262, 263, and 264 can be formedsuch that it can have a FET-type structure. The memory cell-typestructures of select gates 265 and 266 may allow them to be electricallyprogrammed in order to adjust the threshold voltage of the combinationof select gates 261, 262, and 266 and the threshold voltage of thecombination of select gates 263, 264, and 265.

FIG. 16 shows a memory device 1500 including triple drain selecttransistors and triple source select transistors, according to someembodiments described herein. Memory device 1600 can be formed using anycombination of the processes described about with reference to FIG. 5Athrough FIG. 14B. As shown in FIG. 16, memory device 1600 can includeelements similar to or identical to the elements of the memory devicesdescribed above (FIG. 2A through FIG. 14B). Thus, for simplicity, thedescription of the elements of memory device 1600 is not described here.As shown in FIG. 16, each of select gates 262, 264, 265, and 266 can beformed such that it can have a memory cell-type structure, which issimilar or an identical structure of each of the memory cells of memorycell strings 231 and 232. Each of select gates 261 and 263 can be formedsuch that it can have a FET-type structure. The memory cell-typestructures of select gates 262 and 264 may allow them be electricallyprogrammed in order to adjust the threshold voltage of the combinationof select gates 261 and 262 and the threshold voltage of the combinationof select gates 263 and 264.

FIG. 17 through FIG. 2I show processes of forming a memory device 1700including select gates and control lines having different resistances,in which the select gates and control lines include a metal portion,according to some embodiments described herein. Memory device 1700 caninclude elements (e.g., memory cells, select gates, control lines, andother elements, similar to those of the memory devices described abovewith reference to FIG. 2A through FIG. 17. For simplicity, details ofsuch elements are omitted from FIG. 17 through 21.

As shown in FIG. 17, some of the components of memory device 1700 arealready formed. For example, pillars 1731 through 1736 are alreadyformed. Select gates (e.g., source select gates) 1763 and 1764 areformed along segments of pillars 1731 through 1736. Materials (layers ofconductive materials) 1720 are already formed. In additional processes(described below), materials 1720 can be separated at specific locationsto form control lines (e.g., part of access lines) of memory device1700. Materials 1720 can be similar to or the same as the materials(e.g., n-type polycrystalline silicon) of the control lines (e.g.,control lined 220 ₀, 221 ₀, 222 ₀, and 223 ₀) described above withreference to FIG. 2A through FIG. 16.

As shown in FIG. 17, memory cell strings 1741 through 1746 are alsoformed along a segment of a respective pillar among pillars 1731 through1736. Memory cell strings 1741 and 1742 can be similar to memory cellstring 231 and 232 described above with reference to FIG. 2A throughFIG. 16.

As shown in FIG. 17, materials (layers of materials) 1751 and 1752 arealready formed. Materials 1751 and 1752 can be separated in additionalprocesses (described below) to from select gates (e.g., drain selectgates) of memory device 1700. Materials 1751 and 1752 can be similar toor the same as the materials (e.g., n-type or p-type polycrystallinesilicon) of the select gates (e.g., select gates 261 and 262) describedabove with reference to FIG. 2A through FIG. 16. Material (e.g.,dielectric material) 1780 can be formed to allow additional processes,as described below.

FIG. 18 shows memory device 1700 after select gates 1861 and 1862 areformed. Forming select gates 1861 and 1862 can include removing (e.g.,by etching) portions of materials 1751 and 1752 to form openings (e.g.,slits) 1801 through 1807 at selective locations of materials 1751 and1752. As shown in FIG. 18, each of openings 1801, 1803, 1805, and 1807is not symmetrical (asymmetrical) with each of openings 1802, 1804, and1806. For example, the width (from left to right of FIG. 18) each ofopenings 1801, 1803, 1805, and 1807 can be greater than the width (fromleft to right of FIG. 18) of each of openings 1802, 1804, and 1806.Thus, the removed amount of materials 1751 and 1752 in each of openings1801, 1803, 1805, and 1807 can be more than the removed amount ofmaterials 1751 and 1752 in each of openings 1802, 1804, and 1806. Thismeans that materials 1751 and 172 can be asymmetrically removed (e.g.,asymmetrically etched) at selective locations, which are the locationsthat separate one select gate from other (e.g., adjacent) select gates,as shown in FIG. 18. Asymmetrically removing materials 1751 and 1752 mayallow additional processes to be performed in order to cause each ofselect gates 1861 and 1862 to can have conductive materials havingdifferent resistances, as described below.

FIG. 19 shows memory device 1700 after material 1901 is formed inopenings 1801, 1803, 1805, and 1807. Forming material 1901 can includingfilling (e.g., depositing) material 1901 in openings 1801, 1803, 1805,and 1807. Material 1901 can include an oxide material or other materialthat can be relatively easy to be removed (e.g., etched) in additionalprocesses (described below).

FIG. 20 shows memory device 1700 after a block separation process toseparate blocks 2003 ₀ and 2003 ₁. The block separation process canincluding removing materials at edges 2015 and 2016 (e.g., blockboundaries) of to form blocks of memory device 1700, such as blocks 2003₀ and 2003 ₁. FIG. 20 also shows memory device 1700 after control lines2021, 2022, 2023, and 2024 are formed (e.g., formed after materials 1720at edges 2015 and 2016 are removed). FIG. 20 also shows memory device1700 after that material 1901 is removed (e.g. by etching material 1901)from openings 1801, 1803, 1805, and 1807.

FIG. 20 also shows memory device 1700 after recesses 2002 are formed onone side (e.g., formed on only one sidewall) of each of select gates1861 and 1862. Recesses 2002 can also be formed on both sides (e.g.,sides at edges 2015 and 2016) of each of control lines 2021, 2022, 2023,and 2024. Recesses 2002 can also be formed on one side (e.g., formed ononly one sidewall) of each of select gates 1763 and 1764 edges 2015 and2016. As shown in FIG. 20, recesses 2002 may not be formed on sides ofselect gates 1763 that are between two gates 1763 at edges 2015 and2016. Similarly, recesses 2002 may not be formed on sides of selectgates 1764 that are between two gates 1764 at edges 2015 and 2016.

FIG. 21 shows memory device 1700 after portions 2102 are formed.Portions 2102 are formed to improve conductivity (e.g., reduce theresistances) of select gates 1861 and 1862, control lines 2021, 2021,2023, and 2024 two gates 1763 at edges 2015 and 2016, and two selectgates 1764 at edges 2015 and 2016. Each of portions 2102 can includemetal. For example, each of portions 2102 can be an entire metalportion. Alternative, a majority of each of portions 2102 can be metal.Forming portions 2102 can include forming (e.g., deposited bysputtering) a barrier (e.g., thin layer of TiN) in openings 1801, 1803,1805, and 1807. Then, metal material (e.g., W or other conductivematerials) can be formed after the barrier is formed. The metal materialcan be simultaneously formed (e.g., formed by the same process step) inportions 2102. After the metal material (e.g., W) is formed, anadditional separation process can be performed to separate the blocks(e.g., to cut the metal material (e.g., W) at edges 2015 and 2016).

As shown in FIG. 21, each of select gates 1861 can include a portion2101, which is in direct contact with one of portions 2102 (a respectiveportion among portions 2102). In each of select gates 1861, portion 2101is the remaining part of material 1751 (e.g. n-type or p-typepolycrystalline silicon) in FIG. 17 that was not removed when openings1801 through 1807 (FIG. 18) were formed. Thus, each of select gates 1861can include portions (e.g., respective portions 2101 and 2102) havingdifferent resistances. For example, each of portions 2102 (e.g., metal)can have a resistance less than the each of portions 2101 (e.g. n-typeor p-type polycrystalline silicon).

Similarly, in FIG. 21, each of select gates 1862 can include a portion2101, which is in direct contact with one of portions 2102 (a respectiveportion among portions 2102). In each of select gates 1862, portion 2101is the remaining part of material 1752 (e.g. n-type or p-typepolycrystalline silicon) in FIG. 17 that was not removed when openings1801 through 1807 (FIG. 18) were formed. Thus, each of select gates 1862can include portions (e.g., respective portions 2101 and 2102) havingdifferent resistances. For example, each of portions 2102 (e.g., metal)can have a resistance less than the each of portions 2111 (e.g. n-typeor p-type polycrystalline silicon).

As shown in FIG. 21, each of control lines 2021, 2021, 2023, and 2024can include a portion 2111 at edge 2015 that is in direct contact withone of portions 2102 (a respective portion among portions 2102 at edge2015) and a portion 2111 at edge 2016 that is in direct contact with oneof portions 2102 (a respective portion among portions 2102 at edge2016). In each of control lines 2021, 2021, 2023, and 2024, portion 2111at edge 2015 and portion 2111 at edge 2016 are the remaining parts of arespective material 1720 (e.g. n-type polycrystalline silicon) at edges2015 and 2016 in FIG. 20 that were not removed when the block separationprocess (FIG. 20) were performed. Thus, each of control lines 2021,2021, 2023, and 2024 can include portions (e.g., respective portions2111 and 2102 at edges 2015 and 2016) having different resistances. Forexample, each of portions 2102 (e.g., metal) can have a resistance lessthan the each of portions 2111 (e.g. n-type or p-type polycrystallinesilicon).

As shown in FIG. 21, each of select gates 1763 can include a portion2121 at edge 2015 that is in direct contact with one of portions 2102 (arespective portion among portions 2102 at edge 2015) and a portion 2121at edge 2016 that is in direct contact with one of portions 2102 (arespective portion among portions 2102 at edge 2016). In each of selectgates 1763 at edges 2015 and 2016, portion 2121 is the remaining partsof the conductive material (e.g. n-type or p-type polycrystallinesilicon) of select gates 1763 at edges 2015 and 2016 that were notremoved when the block separation process (FIG. 20) were performed.Thus, each of select gates 1763 at edges 2015 and 2016 can includeportions (e.g., respective portions 2121 and 2102 at edges 2015 and2016) having different resistances. For example, each of portions 2102(e.g., metal) can have a resistance less than the each of portions 2121(e.g. n-type or p-type polycrystalline silicon).

Similarly, each of select gates 1764 can include a portion 2121 at edge2015 that is in direct contact with one of portions 2102 (a respectiveportion among portions 2102 at edge 2015) and a portion 2121 at edge2016 that is in direct contact with one of portions 2102 (a respectiveportion among portions 2102 at edge 2016). In each of select gates 1764at edges 2015 and 2016, portion 2121 is the remaining parts of theconductive material (e.g. n-type or p-type polycrystalline silicon) ofselect gates 1764 at edges 2015 and 2016 that were not removed when theblock separation process (FIG. 20) were performed. Thus, each of selectgates 1764 at edges 2015 and 2016 can include portions (e.g., respectiveportions 2121 and 2102 at edges 2015 and 2016) having differentresistances.

FIG. 22 and FIG. 23 show processes of forming a memory device 2200including select gates and control lines having different resistances,in which the select gates and control lines include a silicide portion,according to some embodiments described herein. The structure of memorydevice 2200 in FIG. 22 can be formed using similar or the same processesused to as form memory device 1700 up to the structure of memory device1700 shown in FIG. 20.

FIG. 23 shows memory device 2200 after portions 2302 are formed. Each ofportions 2302 can be in direct contact with a respective portion amongportions 2102, 2111, or 2121. Portions 2302 are formed to improveconductivity (e.g., reduce the resistances) of select gates 1861 and1862, control lines 2021, 2022, 2023, and 2024, two gates 1763 at edges2015 and 2016, and two select gates 1764 at edges 2015 and 2016.

Unlike each of portions 2102 (e.g., a metal portion) in FIG. 2I, each ofportions 2302 in FIG. 23 can be a silicide portion. Forming portions2302 can include performing a silicidation (e.g., partial silicidation)process to form portions 2302 as shown in FIG. 23. Performing thesilicidation process can include forming metal (e.g., Co, Ni, or othermetal materials) material in recesses 2002. Then, an annealing processcan be performed after the metal material is formed in order to formportions 2302.

As shown in FIG. 23, each of select gates 1861 and 1862 can include aportion 2101, which is in direct contact with one of portions 2302 (arespective portion among portions 2302). Thus, each of select gates 1861and 1862 can include portions (e.g., respective portions 2101 and 2302)having different resistances. For example, each of portions 2302 (e.g.,silicide) can have a resistance less than the each of portions 2101(e.g. n-type or p-type polycrystalline silicon).

Each of control lines 2021, 2021, 2023, and 2024 can include a portion2111 at edge 2015 that is in direct contact with one of portions 2302 (arespective portion among portions 2302 at edge 2015) and a portion 2111at edge 2016 that is in direct contact with one of portions 2302 (arespective portion among portions 2302 at edge 2016). Thus, each ofcontrol lines 2021, 2021, 2023, and 2024 can include portions (e.g.,respective portions 2111 and 2302 at edges 2015 and 2016) havingdifferent resistances. For example, each of portions 2302 (e.g.,silicide) can have a resistance less than the each of portions 2111(e.g. n-type or p-type polycrystalline silicon).

Each of select gates 1763 and 1764 can include a portion 2121 at edge2015 that is in direct contact with one of portions 2302 (a respectiveportion among portions 2302 at edge 2015) and a portion 2121 at edge2016 that is in direct contact with one of portions 2302 (a respectiveportion among portions 2302 at edge 2016). Thus, each of select gates1763 and 1764 can include portions (e.g., respective portions 2121 and2302 at edges 2015 and 2016) having different resistances. For example,each of portions 2302 (e.g., silicide) can have a resistance less thanthe each of portions 2121 (e.g. n-type or p-type polycrystallinesilicon).

FIG. 24 shows a memory device 2400, which can be a variation of memorydevice 1700 of FIG. 21 or memory device 2200 of FIG. 23. As shown inFIG. 24, memory device 2400 can include portions 2402. Each of portions2402 can be in direct contact with a respective portion among portions2121 of each of select gates 1763 and 1764. Thus, in memory device 2400,select gates 1763 and 1764 at edges 2015 and 2016, and select gates 1763and 1764 between edges 2015 and 2016 can have portions 2402 and 2121.This is unlike memory device 1700 of FIG. 21 and memory device 2300 ofFIG. 23 where only select gates 1763 and 1764 at edges 2015 and 2016have portions of different resistances (e.g., portions 2102 and 2121 inFIG. 21, and portions 2302 and 2121 in FIG. 23).

In FIG. 24, forming portions 2402 can include processes similar to thoseused to form portions 2102 (FIG. 21) of memory device 1700 or processessimilar to those used to form portions 2302 (FIG. 23) of memory device2200. For example, in FIG. 24, before forming elements located aboveselect gates 1763 and 1764 (e.g., memory cell strings 1741 through 1746,control lines 2021, 2021, 2023, and 2024, and select gates 1861 and1862), processes similar to processes of forming portions 2102 (e.g.,metal portions) of memory device 1700 (FIG. 21) can be used to formportions 2402 of memory device 2400 of FIG. 24. Alternatively, beforeforming elements located above select gates 1763 and 1764, processessimilar to processes of forming portions 2302 (e.g., silicide portions)of memory device 2200 (FIG. 23) can be used to form portions 2402 ofmemory device 2400 of FIG. 24. Thus, each of portions 2402 in selectgates select gates 1763 and 1764 of memory device 2400 can be either ametal portion (e.g., similar to each of portions 2102 of FIG. 21) or asilicide portion (e.g., similar to each of portions 2302 of FIG. 23).

FIG. 24 also shows memory device 2400 include portions 2404. Each ofportions 2404 can be either a metal portion or a silicide portion. Forexample, portions 2404 can be formed using processes similar to thosedescribed above with reference to FIG. 17 through FIG. 21, such thateach of portions 2404 can be a metal portion (e.g., similar to portion2102 of FIG. 21). In another example, portions 2404 can be formed usingprocesses similar to those described above with reference to FIG. 22 andFIG. 23, such that each of portions 2404 can be a silicide portion(e.g., similar to portion 2302 of FIG. 23). Thus, in memory device 2400,each of select gates 1861 and 1862 can include a polycrystalline portion(e.g., one portions 2101) and either a metal or silicide portion (e.g.,one of portions 2404). Similarly, each of control lines 2021, 2021,2023, and 2024 can include a polycrystalline portion (e.g., one portions2111) and either a metal or silicide portion (e.g., one of portions2404).

The biasing techniques similar to or identical those used in the memorydevices described above (e.g., memory devices 200 and 300 describedabove with reference to FIG. 2A through FIG. 3G) may be used in thememory devices of FIG. 5A through FIG. 24. Thus, besides improvements instructures (e.g., reduced resistances at drain and sources select gatesand control lines described above with reference to shown in FIG. 5Athrough FIG. 24), the memory devices of FIG. 5A through FIG. 24 can alsoinclude improvements in operations (e.g., biasing techniques) similar tothose of memory devices 200 and 300 described above with reference toFIG. 2A through FIG. 3G.

The illustrations of apparatuses (e.g., memory devices 100, 200, 300,400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1700,and 2200) and methods (e.g., operating methods associated with memorydevices memory devices 100, 200, 300, 400, 500, 600, 700, 800, 900,1000, 1100, 1200, 1300, 1400, 1500, 1700, and 2200, and methods (e.g.,processes) of forming these memory devices) are intended to provide ageneral understanding of the structure of various embodiments and arenot intended to provide a complete description of all the elements andfeatures of apparatuses that might make use of the structures describedherein. An apparatus herein refers to, for example, either a device(e.g., any of memory devices 100, 200, 300, 400, 500, 600, 700, 800,900, 1000, 100, 1200, 1300, 1400, 1500, 1700, and 2200) or a system(e.g., a computer, a cellular phone, or other electronic system) thatincludes a device such as any of memory devices 100, 200, 300, 400, 500,600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1700, and 2200.

Any of the components described above with reference to FIG. 1 throughFIG. 24 can be implemented in a number of ways, including simulation viasoftware. Thus, apparatuses (e.g., memory devices 100, 200, 300, 400,500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1700, and2200 or part of each of these memory devices, including a control unitin these memory devices, such as control unit 116 (FIG. 1), and theselect circuits 241 through 252) described above may all becharacterized as “modules” (or “module”) herein. Such modules mayinclude hardware circuitry, single and/or multi-processor circuits,memory circuits, software program modules and objects and/or firmware,and combinations thereof, as desired and/or as appropriate forparticular implementations of various embodiments. For example, suchmodules may be included in a system operation simulation package, suchas a software electrical signal simulation package, a power usage andranges simulation package, a capacitance-inductance simulation package,a power/heat dissipation simulation package, a signaltransmission-reception simulation package, and/or a combination ofsoftware and hardware used to operate or simulate the operation ofvarious potential embodiments.

Memory devices memory devices 100, 200, 300, 400, 500, 600, 700, 800,900, 1000, 1100, 1200, 1300, 1400, 1500, 1700, and 2200 may be includedin apparatuses (e.g., electronic circuitry) such as high-speedcomputers, communication and signal processing circuitry, single ormulti-processor modules, single or multiple embedded processors,multicore processors, message information switches, andapplication-specific modules including multilayer, multichip modules.Such apparatuses may further be included as subcomponents within avariety of other apparatuses (e.g., electronic systems), such astelevisions, cellular telephones, personal computers (e.g., laptopcomputers, desktop computers, handheld computers, tablet computers,etc.), workstations, radios, video players, audio players (e.g., MP3(Motion Picture Experts Group. Audio Layer 3) players), vehicles,medical devices (e.g., heart monitor, blood pressure monitor, etc.), settop boxes, and others.

The embodiments described above with reference to FIG. 1 through FIG. 24include apparatuses and using first and second select gates coupled inseries between a conductive line and a first memory cell string of amemory device, and third and fourth select gates coupled in seriesbetween the conductive line and a second memory cell string of thememory device. The memory device can include first, second, third, andfourth select lines to provide first, second, third, and fourthvoltages, respectively, to the first, second, third, and fourth selectgates, respectively, during an operation of the memory device. The firstand second voltages can have a same value. The third and fourth voltagescan have different values. Other embodiments including additionalapparatuses and methods are described.

In the detailed description and the claims, a list of items joined bythe term “at least one of” can mean any combination of the listed items.For example, if items A, B, and C are listed, then the phrase “at leastone of A. B and C” can mean A only: B only; C only; A and B; A and C; Band C; or A, B, and C.

The above description and the drawings illustrate some embodiments ofthe invention to enable those skilled in the art to practice theembodiments of the invention. Other embodiments may incorporatestructural, logical, electrical, process, and other changes. Examplesmerely typify possible variations. Portions and features of someembodiments may be included in, or substituted for, those of others.Many other embodiments will be apparent to those of skill in the artupon reading and understanding the above description.

What is claimed is:
 1. An apparatus comprising: a pillar extendingbetween a first conductive region and a second conductive region, thepillar including a first segment, a second segment, a third segment, anda fourth segment, the second and third segments being between the firstand fourth segments; a first conductive material located on a firstlevel of the apparatus and opposite from the first segment of thepillar, the first conductive material having a first thickness; a secondconductive material located on a second level of the apparatus andopposite from the second segment of the pillar, the second conductivematerial having a second thickness; a third conductive material locatedon a third level of the apparatus and opposite from the third segment ofthe pillar, the third conductive material having a third thickness, thefirst thickness being greater than each of the second and thirdthicknesses; and a memory cell string including memory cells locatedalong the fourth segment of the pillar.